The purpose of this study was to examine the effects of polycystic ovary syndrome (PCOS) and body mass index (BMI) on selected indicators of IVF or intracytoplasmic sperm injection (ICSI) treatment success. A retrospective cohort study was conducted using existing data on 69 IVF/ICSI treatment cycles undergone by PCOS women and an individually matched sample of 69 IVF/ICSI treatment cycles undergone by non-PCOS women at a major fertility treatment centre. BMI (kg/m(2)) was analysed as a continuous and categorical (<25, 25-29.9, > or =30)variable. Results indicated that PCOS was directly associated with the number of oocytes retrieved. Irrespective of PCOS status, continuous BMI was inversely associated with total and mature oocytes retrieved. Multiple linear regression analyses indicated no significant effects of PCOS or continuous BMI on the number of mature oocytes fertilized per mature oocyte retrieved or inseminated. Similarly, multiple logistic regression analyses suggested no significant effect of PCOS and continuous BMI on the odds of pregnancy, miscarriage or live birth. Furthermore, categorical BMI did not influence process and outcome measures of IVF/ICSI treatment success. PCOS and continuous BMI appear to have significant and distinct effects on early stages, but not on later stages, of IVF/ICSI treatment.