Irreligious people make 6,8% of Lithuanian population. They may roughly be divided into multiple groups: rigorous followers of science, agnostics, and radical leftist atheists. This last group, disproportionally represented in media, seeks to limit the rights of the religious and promotes some scientifically disproven theories.
Beyond these groups, the religious-irreligious line is blurry at best. Some followers of religious-in-nature beliefs also style themselves irreligious, while many others associate themselves with a faith but practice it only occasionally or partially.
The key of explaining these paradoxes lies in the Soviet occupation (1940-1990). Before it (in the 1930s) virtually everybody in Lithuania followed some religion. The Soviet atheist regime, however, sought to eradicate the faith through discrimination and propaganda. "Atheism" became a subject taught in universities and even had museums dedicated to it; it was a necessity for climbing the tightly controlled career ladder. The "Soviet irreligiousness" was, however, in a sense a fundamentalist faith by itself. A "good atheist" was expected not to question any Marxist-Leninist doctrines; those who did, used to be forcibly "treated" in psychiatric wards. Radical leftist atheism of today's Lithuania, in essence, follows this tradition although European far left now replaces Soviet communism as the source of inspiration.
The decades of anti-religious propaganda (with e.g. extensive education on the millennium-old Crusades but none at all on the millions recently murdered in Soviet genocides) made the word "religion" itself controversial to some, so many post-Soviet religious movements (and their followers) avoid it.
The strong atheism-collaboration link made irreligiousness socially unacceptable while the Soviet occupation continued. Following Christian rites was a form of defiance. Few ethnic Lithuanians abandoned their religion but the church closures, textbook shortages, and discrimination impeded regular worship and passing the faith to children, making the Soviet-born generations less religious. Additionally, many irreligious Russian and Russophone settlers were moved in.
After independence (1990) state atheism was replaced by religious freedom. Large numbers of the irreligious re-found their forefathers' faiths or converted to new religious movements. Atheism has been especially shrinking among the Soviet settler communities where it had been the most prevalent (~26% irreligious in 2001, ~12% in 2011) but also in the population as a whole (10,5% in 2001, 6,8% in 2011). Currently, Jews are the most irreligious ethnicity (43,5%) and Poles are the least irreligious (1,7%). Northeastern Samogitia is the most irreligious region of Lithuania (~11%), followed by the main cities (8%-10%). Other municipalities have 1% to 6% non-believers.