['A large proportion of patients undergoing ICSI have been shown to have an increased sperm aneuploidy rate. This study was undertaken to evaluate the impact of sperm aneuploidy on ICSI outcome.', 'To accomplish this, 48 consecutive unselected male patients (median age 34 years) had their sperm aneuploidy rate evaluated in the same swim-up preparation used for ICSI. Chromosomes 8, 12, 18, X and Y were evaluated by fluorescence in-situ hybridization. Patients were divided into two groups (A and B) based on the sperm aneuploidy frequency in their sperm. Group A had values below and group B above the upper limit of normal [1.55%, determined in 14 healthy men (median age 25 years) with normal semen parameters by WHO 1999 criteria (control group)].', 'Group A consisted of 12 patients (25%) whose sperm aneuploidy rates fell below the cut-off value of the control group (median 1.25%; range 0.85-1.52). Group B consisted of the remaining 36 patients (75%), who had an elevated sperm aneuploidy rate (median 3.25%; range 1.64-23.60). Fertilization (93 versus 85%) and cleavage (100 versus 98%) rates were similar for both groups. Group A had significantly higher clinical pregnancy (75 versus 34%; P < 0.001) and implantation (34 versus 13%; P < 0.001) rates compared with group B. In addition, group A had a lower overall miscarriage rate (11.1 versus 38.9%). Other factors that affect pregnancy and implantation, such as patient age and conventional semen parameters, were similar for both groups.'] Is lower sperm aneuploidy frequency associated with high pregnancy rates in ICSI programmes?