This study compared the physical performance of adolescents in 1997 and 1968. The material included 1329 15-year-old Norwegian adolescents in Akershus county in Norway in 1968, and 1105 15-year-old adolescents in the same region in 1997. The investigations were supervised by the same conductor on both occasions, and used identical physical tests. The test battery included dynamic endurance of abdominal and low back muscles, hip flexion, ankle dorsiflexion and aerobic fitness. Compared with 1968, low back extension endurance in 1997 was almost 10% lower in both genders, the endurance of the abdominal muscles was 4.8% poorer among boys and 8.1% higher among girls and the ratio between abdominal and low back extension endurance was 11.8% higher among boys and 26.4% higher in girls. Compared with 1968, hip flexion in 1997 was 8.3% higher in girls, while ankle dorsiflexion and aerobic fitness in boys were 15% and 13.4% poorer, and 4.8% poorer and 2.5% higher in girls, respectively. The data indicate a general decline during one generation in physical performance among boys, a decline in low back endurance, truncus balance and ankle mobility among girls and in a higher abdominal endurance among girls.