The purpose of this study was to compare the maximal oxygen uptake (VO2max) in 18-19-year-old Norwegian men from 1980 to 1985 and 2002. In addition, we investigated the relationship between VO2max and education and smoking habits in the sample from 2002. From 1980 to 1985, VO2max was predicted using the Astrand-Rhyming bicycle test for 183 610 eighteen-year-old Norwegian men (91% of the male Norwegian population in this age group). In 2002, the same test was performed on a representative sample of the same age population (N=1028). VO2max (mL x kg(-1)x min(-1)), decreased by 8%, body weight increased by 7% and body mass index (BMI) increased by 6% over the approximately 20-year period (P<0.01). Results from the 2002 sample revealed that smokers had a lower VO2max than non-smokers and vocational students had a lower VO2max than academic students (P<0.05). The average reduction in VO2max was because of an increased number of men with low or very low VO2max, and a reduced number of men with high VO2max values. This is of particular concern since the prevalence of lifestyle-related diseases is higher in groups with low VO2max.