The purpose of this study was to assess the limits of hamstring tightness in 369 children by using three common tests. The straight leg-raise test averaged 100 degrees at birth, increasing to 110 degrees at age 1 year, before decreasing to 80 degrees by age 5-6 years. It then remained constant to skeletal maturity. Hamstring tightness is present if this angle is < 80 degrees in children younger than 2 years. After this age, the limit decreased steadily to plateau at 60 degrees by the age of 6 years. The popliteal angle measured the maximum 180 degrees from birth to age 2 years. This angle then decreased to average 155 degrees by age 6 years and remained steady. An angle < 125 degrees suggests significant hamstring tightness. The touching-toes test showed minimal variation between age groups averaging, 1 +/- 3 cm. Distances reached < -5 cm in children aged up to 6 years and < -15 cm in those older than 6 indicate excessively tight hamstrings. Little difference was seen between sides, although girls demonstrated less hamstring tightness. All tests showed a positive correlation with the grade of ligamentous laxity, but no association with the child's stage of puberty could be detected.