This is a retrospective study to investigate whether motivational interviewing increases weight loss among obese or overweight women prior to fertility treatment. Women with body mass index (BMI) > 30 kg/m(2) approaching the Fertility Clinic, Regional Hospital Skive, were given advice about diet and physical activity with the purpose of weight loss. In addition, they were asked if they wanted to receive motivational interviewing. Among other data, age, height and weight were obtained. Main outcomes were weight loss measured in kg and decrease in BMI. We studied 187 women: 110 received sessions of motivational interviewing (intervention group, n = 110), 64 received motivational support by phone or e-mail only and 13 women did not wish any motivational support (control group, n = 77). The mean weight loss and decrease in BMI was greater in the intervention group compared with the control group (9.3 kg versus 7.3 kg, difference p = 0.01, 3.3 kg/m(2) versus 2.6 kg/m(2), difference p = 0.02). The mean period of intervention was comparable in the two groups, 7.9 month and 7.3 month, respectively, (difference non significant: NS). The study indicates that motivational interviewing may be a valuable tool in weight loss programs for obese and overweight women prior to fertility treatment.