We determined the rates of neural tube defects at a referral hospital in Gorgan, north Islamic Republic of Iran, and the relations of these abnormalities to sex, maternal ethnicity, maternal age and season. During 1998-2003, there were 109 cases among 37951 births, a prevalence of 28.7 per 10000 (24.8 and 32.8 per 10000 among males and females respectively). The rates in Turkmen, native Fars and Sistani ethnic groups were 40.5, 25.2 and 30.8 per 10000 respectively. The rates of spina bifida and anencephaly were 16.3 and 11.3 per 10000 respectively. The rate of affected newborns was highest in mothers aged over 35 years (50.7 per 10000). The peak prevalence was in December
