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Objective: The main objective of the present study was to determine whether the summer season is a risk factor for oligohydramnios, by comparing the frequency of oligohydramnios during the summer months versus its frequency during the rest of the year., Methods: A retrospective population-based study including all pregnancies of patients with oligohydramnios that delivered during the years 1988-2007 in a tertiary medical center was performed. All non-idiopathic causes for oligohydramnios were excluded from the analysis. Summer months were defined as May to August. A multiple logistic regression model was performed in order to control for confounders., Results: During the study period, there were 191,558 deliveries of which 4,335 were diagnosed with oligohydramnios. Of these, 1,553 deliveries occurred during the summer months and 2,782 deliveries occurred during the rest of the year. Higher rates of oligohydramnios were found in the summer months as compared to the rest of the year: 2.5 versus 2.1%, odds ratio (OR) = 1.18, 95% confidence interval (CI) 1.1-1.3; P < 0.001. Using a multiple logistic regression model, controlling for confounding variables such as ethnicity, the summer season was noted as an independent risk factor for oligohydramnios (OR = 1.1, 95% CI 1.02-1.21; P < 0.001). Another independent risk factor for oligohydramnios was Bedouin ethnicity (OR = 1.3, 95% CI 1.2-1.4; P = 0.015)., Conclusions: Oligohydramnios is significantly more common during the summer months versus the rest of the year. Moreover, the summer season is an independent risk factor for oligohydramnios.