To determine the effect of long-term storage on cryopreserved human sperm, 238 individual samples from 34 cryopreserved sperm deposits that had been collected between 1976 and 1989 were evaluated at regular intervals. The material was from 34 patients, 18 of whom suffered from underlying malignant disease. Every 3 years a sample from each deposit was thawed for microscopic analysis. During the course of the storage period limited to a maximum of 21 years, all ejaculate parameters had deteriorated in comparison to fresh semen. Quantitative motility was the most sensitive parameter with a decrease of ca. 80%. Sperm density decreased hardly at all. The parameters of the criteria investigated did not decrease linearly or proportionally with the storage duration, but rather more directly after the freezing process or within the first 3 years. These changes became increasingly smaller as the storage time lengthened. Almost all of the deposits exhibited adequate quality at all times during storage. Consequently, 21-year permanent frozen storage in liquid nitrogen is safe regarding aspects of spermatology.