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Background and Objective: Cryptorchidism or undescending testis is a developmental defect and occurred in 2-4% of male newborns. This study was done to determine the pattern and risk factors of cryptorchidism in Gorgan, northern Iran. Methods: In this cohort study, 2851 male newborns were examined for cryptorchidism at the birth and follow up for one year after birth in Dezyani referral teaching hospital in Gorgan, northern Iran during April 2010 - December 2011. Mother ethnicity, working in farmland, addiction, consanguinity, age, infant maturity and birth weight were recorded for each subject. Results: The rate of cryptorchidism was 18.9 per 1000 live birth. Bilateral and unilateral cryptorchidism was 11.7 and 7.1 per 1000, respectively. The rate of cryptorchidism in preterm newborns (30 per 1000) was significantly higher than the term (20 per 1000) and post term (11.4 per 1000) newborns (P<0.05). The Mean±SD of newborns weight with unilateral cryptorchidism (3024±537grams) was significantly lower than the healthy newborns (3253±489 grams) (P<0.05). The rate of cryptorchidism in Turkmens (10 per 1000 births) was significantly lower than Fars (21 per 1000 births) and Sistani (23 per 1000 births) newborns (P<0.05). One year Follow up of newborns showed that 41 (77.3%) testes were descent to scrotum. Conclusion: Low births weight, prematurity and ethnicity are the main risk factors of cryptorchidism in northern Iran.