Obesity can affect ovulation and the chances of pregnancy. In this prospective study, a weight loss programme was assessed to determine whether it could help infertile overweight anovulatory women to establish ovulation and assist in achieving pregnancy, ideally without further medical intervention. The subjects acted as their own historical controls. They underwent a weekly programme of behavioural change in relation to exercise and diet over 6 months; those who did not complete the 6 months were treated as the comparison group. Women in the study group lost an average of 6.3 kg, with 12 of the 13 subjects resuming ovulation and 11 becoming pregnant, five of these spontaneously. Fitness, diet and psychometric measurements all improved. Fasting insulin and testosterone concentrations dropped significantly, while sex hormone binding globulin concentrations rose. None of these changes occurred in the comparison group. Thus, weight loss with a resultant improvement in ovulation, pregnancy outcome, self-esteem and endocrine parameters is the first therapeutic option for women who are infertile and overweight.