[1] The PSU received 11% of the vote in the 1978 elections, winning seven seats.
It subsequently joined the governing coalition alongside the Sammarinese Socialist Party (PSS) and the Sammarinese Communist Party (PCS).
[2] PSU sent three delegates to the congress of the Socialist International in 1980; Pier Paolo Gasperoni, Emilio della Balda and Dominique Morolli.
In the mid-1980s the party was renamed Unitary Socialist Party–Socialist Agreement.
It won eight seats again in the 1988 elections, emerging as the third-largest party.