It is well-documented that male overweight and obesity causes endocrine disorders that might diminish the male reproductive capacity; however, reports have been conflicting regarding the influence of male body mass index (BMI) on semen quality and the outcome of assisted reproductive technology (ART). The aim of this study was to investigate whether increased male BMI affects sperm quality and the outcome of assisted reproduction in couples with an overweight or obese man and a non-obese partner. Data was prospectively collected from 612 infertile couples undergoing ART at a Danish fertility center. Self-reported information on paternal height and weight were recorded and BMI was calculated. The men were divided into four BMI categories: underweight BMI < 20 kg m(-2) normal BMI 20-24.9 kg m(-2), overweight BMI 25-29.9 kg m(-2) and obese BMI > 30 kg m(-2). Conventional semen analysis was performed according to the World Health Organization guideline and sperm DNA integrity was analyzed by the Sperm Chromatin Structure Assay (SCSA). No statistically significant effect of male BMI was seen on conventional semen parameters (sperm concentration, total sperm count, seminal volume and motility) or on SCSA-results. Furthermore, the outcome of ART regarding fertilization rate, number of good quality embryos (GQE ), implantation and pregnancy outcome was not influenced by the increasing male BMI.