In recent years, sex differences in mortality have followed diverse patterns of change in developed countries. As there is no analogous evidence from Poland, the aim of this study was to describe the pattern of change in excess male mortality among Polish inhabitants aged 35–64 during 1995–2002, when the major socioeconomic transformation occurred, and compare it with sex differences in mortality observed in the late 1980s. During the study period, excess male mortality decreased significantly, independently of age and educational level. The reduction in mortality was observed in both sexes, but its magnitude was greater in men. These changes resulted mainly from a reduction in mortality rates due to cardiovascular disease and lung cancer in males and a concomitant increase in mortality rates due to lung cancer and suicides in females. Although, in general, excess male mortality decreased, social gradients related to this phenomenon increased. Subjects (in particularly men) who had graduated from university benefited the most, their magnitude of reduction in mortality rates being the greatest. Changes in social environment during the transformation period in Poland are suggested as major determinants of these changes, but further studies are needed.