Sperm morphology has always been considered an important tool in evaluating a man's fertilizing potential. The objective of this multicentric study was to evaluate intra- and interindividual variability and between-laboratory variation using the same or different criteria of sperm morphology assessment. Semen samples were obtained from 20 males and 32 smears were made of all samples. Eighty coded smears (4 per patient) were sent to 8 laboratories for morphology assessment. The centers applied different classification systems (strict criteria, WHO 1987, Düsseldorf criteria) and participants were asked to analyze the 80 smears twice, with an interval of 1 week between each participant's two analyses. Intraclass correlations between repeats showed that sperm morphology can be assessed with acceptable within observer reproducibility. Expected increases in imprecision were observed up to coefficients of variation of >30% with decreasing morphology scores, regardless of the classification system used. Agreement in correct classification of samples as normal/abnormal was obtained in 80% of cases. Differences in reproducibility between slides may reflect an important source of heterogeneity due to smear preparation. These results emphasize the importance of external quality control systems to improve the value of sperm morphology assessments in the investigation of the male partner in a subfertile couple.