The latter include the Winter War of 1939-40, the Continuation War of 1941-44 and the Lapland War of 1944-45.
In Lappeenranta, near the Russian border, the remains of 37 soldiers recovered from the Karelian Isthmus and other areas of Karelia that are now part of the Russian Federation were buried on the grounds of Lappee Church.
Only one of them had been identified. Defence Minister Jyri Häkämies took part in the burials, which were preceded by a Lutheran service.
Since an agreement in 1992 between Finland and Russia, a state-supported Finnish association has been searching for remains of Finnish soldiers in Eastern Karelia, Russia, and bringing them back to Finland for burial.
So far the group has repatriated remains from 1,100 soldiers. About 300 of these have been identified.
An estimated 11,000-13,000 Finnish troops were either lost on the battlefields or reported missing during the wars fought between 1939 and 1945.
Memorial Day has been observed since 1940. Until 1995, flags were flown at half-staff on the third Sunday of May, but now are raised fully.
In Helsinki, President Tarja Halonen laid a wreath at the Heroes' Cross in Hietaniemi Cemetery, as did representatives of veterans' groups and others.