Introduction: Even though an increase in the number of hospital admissions for manic and depressive periods at certain times of the year is reported in bipolar disorder (BD), mood symptoms do not show a seasonal variation. We aimed to find out the possible causes of increased hospital admissions of BD patients in certain periods of the year.Method: The study was carried out in four centers in Turkey. The patient group consisted of 41 persons with a diagnosis of BD in remission. The healthy control (HC) group consists of 37 persons. The selected evaluation times are fall equinox (September 23), spring equinox (March 21), summer solstice ( June 21) and winter solstice (December 21). For mood symptoms, Hamilton Depression Rating Scale and Young Mania Rating Scale; for functioning Functioning Assessment Short Test; for neurocognitionStroopTest(ST)andReyAuditoryVerbalLearningTest (RAVLT), for biological rhythm Biological Rhythms Interview of AssessmentinNeuropsychiatry,andSeasonalPatternAssessmentQuestionnaire were used.Results: In terms of mood symptoms no seasonal variation was found. Across all four periods of assessment of BD group, statistically significant variation was only observed in the instant recall, learning and recognition domains of RAVLT and word test and color test domains of ST; however, it was not sufficient to distinguish the BD group separating from the control group.Conclusions: In terms of mood symptoms, psychosocial functionality, biologicalrhythm,neurocognition,noseasonalvariationwasdemonstrated that could distinguish the BD group from the HC group.