SummaryIn a retrospective blind study, Papanicolaou's stained semen smears of the husbands of 105 patients who took part in thein vitrofertilization/embryo transfer (IVF/ET) program of the Department of Gynecology and Obstetrics at the Heinrich Heine University Düsseldorf in 1991, were evaluated for the rates of normal sperm heads. The patients were divided into three groups according to the results of the IVF/ET: A = no fertilized egg; B = only fertilization, no pregnancy; C = pregnancy/birth. Four different categories of the sperm heads' morphology were defined: 1) ‘Ideally’ normal heads (normal size, relations width to length 2/3 to 3/5, acrosomal region ≥40≤70%); 2) Normal heads with only minor deviations from the ‘ideally’ normal form, strictly excluding spermatozoa with inhomogeneously stained acrosomal or pointed post‐acrosomal regions; 3) Sperm heads with major alterations which are nevertheless widely considered as still normal in the literature; 4) Heads which are generally accepted as pathologically formed. It could be shown that the application of the strict criteria in the categories 1 plus 2 lead to significant differences not only between the IVF/ET groups A and B or C, but also between the