PURPOSE: Although the association between nocturia and depressive symptoms has been demonstrated, the causal direction remains unclear. We investigated the directional association between nocturia and depressive symptoms using longitudinal data from the general population. MATERIALS AND METHODS: This longitudinal analysis was conducted as part of the Nagahama Cohort Project, a population based cohort study, with baseline and 5-year followup investigations. Nocturnal voiding frequency and mental health were measured with self-report questionnaires, the International Prostate Symptom Score and the 5-item Mental Health Inventory. Logistic regression analyses and a cross-lagged panel analysis were performed to analyze the bidirectional association between nocturia and depressive symptoms. RESULTS: With 9,764 participants at baseline, data from 8,285 were used in this analysis. Median age at baseline was 57.3 years and the proportion of men was 32.0%. New onset depressive symptoms and nocturia were observed among 369 and 793 participants, respectively. In adjusted logistic regression analyses we observed a clear dose-relationship between baseline nocturnal voiding frequency and new onset depressive symptoms (p for trend <0.001) and a weak association between baseline 5-item Mental Health Inventory and new onset nocturia (p for trend=0.0087). In a cross-lagged panel analysis the path coefficient from nocturnal voiding frequency to 5-item Mental Health Inventory (β=-0.06, p <0.001) was stronger than that from 5-item Mental Health Inventory to nocturnal voiding frequency (β=-0.02, p=0.047). CONCLUSIONS: This longitudinal study demonstrated a bidirectional association between nocturia and depressive symptoms. The cross-lagged path coefficient suggested that nocturia could more likely be a cause than a result of depressive symptoms.