To describe the reproductive outcome in women with incidental diagnosis of septate uterus at first trimester scan. G1 pregnant women attending our center for a routine viability scan (6–9 wks) who were found to have subseptate or septate uterus were prospectively included in the study. A mullerian anomaly was initially suspected at 2D ultrasound whereas the conclusive diagnosis of septate uterus was subsequently carried out by 3D ultrasound. A detailed follow up of the pregnancy was obtained in all cases Overall 18 patients with a single intrauterine viable pregnancy and a diagnosis of septate uterus at a median gestational age of 7 weeks were included in the study. Livebirth rate was extremely poor (27.7%) due to the occurrence of early (< 13 weeks) or late miscarriage (14–22 weeks) respectively in 9 and 5 cases. Pregnancy outcome is expected to be poor if a septate uterus is incidentally diagnosed in the early stage of a viable intrauterine pregnancy.