Several reports have suggested that sperm counts of normal men have declined in many geographical regions during the last decades. Deterioration of sperm morphology has also been reported in some studies covering long sample collecting periods. The original semen analysis data of our semen laboratory from the period 1980--1994 showed a significant decline in the proportion of spermatozoa with normal morphology. The finding was, however, questioned because of changes in sperm morphology assessment criteria during the study period. In the present study 1745 smears were re-analysed to cover evenly the whole study period. The samples were examined in random order by using strict assessment criteria. Multiple linear regression analysis of the re-analysed data showed no effect of the year of sample delivery on sperm morphology between the years 1980 and 1994. However, there was a significant decline in the proportion of normal spermatozoa with later year of men's birth.