With the restoration of independence, compulsory health insurance was introduced in Poland for every employed person. Health insurance funds were then established. In Vilnius there was the Social Insurance Office, which had its own building designed by Warsaw architects.

Insurance system in the Second Republic
. After Poland regained independence, efforts were made to establish an insurance institution to provide medical assistance in case of illness and benefits in case of inability to work. Before World War I, such a function had been performed in the Prussian partition and Galicia by health insurance funds (the name was a linguistic carbon copy of the German Krankenkasse), while in the Russian partition there was in fact no such institution. By virtue of a decree issued by the Provisional Head of State Józef Piłsudski on 11 January 1919, and made more specific by a law of 19 May 1920 on compulsory insurance in the event of illness, health insurance was introduced for all employees. This was followed by the establishment of district health insurance funds. By 1928, 243 such institutions had been organised throughout the country.

An employee was assigned to a fund that operated in the area he or she resided. Insurance was compulsory and included full funding for the treatment of the insured and his or her family, hospitalisation, provision of medicines, as well as payment of sickness and maternity benefits and funeral benefits. The funds provided health care by contracting with hospitals and doctors to treat their members, but often created and operated their own medical facilities in the nature of clinics or even hospitals.

Importance of health insurance funds
The importance of the health insurance funds was immense, as they made qualified medical assistance available to the public, who until then had largely relied on quacks, midwives and feldspersons. Over time, however, problems in the functioning of such an institution became apparent (including accusations by medical circles of underestimating the real costs of medical services and inflating premiums while providing low benefits). These led to a reduction in the number of funds to around a hundred, followed by a reform of social insurance. The Act of 28 March 1933 on social insurance involved the replacement of the sickness funds with social insurances; in addition, the Social Insurance Institution (ZUS) was established as the institution regulating the national insurance system.

Building of the Vilnius Social Insurance Institute
. In 1937-1938, construction of the Social Security Building in Vilnius was underway on the basis of the winning competition design by two Warsaw architects, Stanisław Murczyński (1906-1974) and Jerzy Sołtan (1913-2005). One of the largest buildings in the city between the wars, it stood on the representative Mickiewicza Street (today's Gediminas Avenue), at the junction with Dąbrowskiego Street (today's Jakštasa Street), a short distance from the banking facilities built at the time.

Architecture of the Vilnius Social Security Building
. The building of the Social Insurance Institution, laid out on an L-shaped plan, consists of the main part planned on Mickiewicza Street and a side wing on Dąbrowskiego Street. The dominant, five-storey body of the main part was solved in the monumental convention with the use of elements typical of the functionalist trend, among others, the principles defined by Le Corbusier. The ground floor area was clearly demarcated with rustic granite cladding. On the other hand, the part facing Dąbrowskiego Street, which housed the entrance area, was heavily undercut and supported on pillars. The façade on this side serves as the façade and was therefore designed in the most expressive manner: the narrower left side is clad with smooth stone slabs, while the right side is of a skeleton construction with window openings. The two parts of the façade are juxtaposed in a contrasting manner. In this way, the idea of creating visual effects with different materials and textures, which was important for modernist architecture, was realised.

The side façade facing Mickiewicza Street has a regular arrangement of window openings, enlivened by modest rectangular panels in the spaces between the windows. The monumental element was obtained by means of raw stone cladding (sandstone). The whole is enclosed by a rather distinctive cornice. Above it, a "ship-like" steel balustrade was introduced, betraying the utilitarian character of the roof. The functionalist repertoire of forms is completed by an antenna mast located in the left part of the façade.

The side wing, lower by one storey, is a modest block with smooth facades covered with stucco and regularly divided by window openings. Its main accent is the curved, cantilevered canopy over the side entrance.

The interiors are furnished in a modern manner, but not without luxurious elements. The building is currently used as a healthcare facility.