Little information is available regarding the epidemiology of young onset insulin-requiring diabetes mellitus (IRDM). We described the incidence of young onset IRDM and its trend in males and females of Dhaka, Bangladesh. Subsequently, factors related to possible sex difference were investigated. Young onset IRDM was defined as diabetic patients aged 18–30 years who required three months or more insulin treatment but presented no ketonuria. Between 1994 to 2003, 1,804 cases were registered. Incidence rates were calculated with denominators based on the population census 2001. The overall annual incidence of young onset IRDM for the period 1994–2003 was 8.5 per 100,000 persons (95% CI: 7.2–7.9), and the corresponding value for females (10.9 per 100,000 persons, 95% CI: 9.2–12.1) was higher than that in males (6.7 per 100,000 persons, 95% CI 5.6–7.9). The incidence rate significantly increased in females during the investigated period, but not in males (p for sex interaction < 0.01). There was a significantly higher increment of female cases with a body mass index = 25.0 kg/m2 (overweight/obesity) (19 percentage point) compared to that of males (3 percentage point) between 1994–1998 and 1999–2003 (p for sex interaction < 0.01). The incidence of young onset IRDM is increasing in the Dhaka City population among females, which is attributed to the increase in overweight/obese female cases.