A randomly selected sample of 3494 children evenly representing a total population of 37 391 schoolchildren aged between eleven and twelve was screened for idiopathic scoliosis by the bending test. Ten per cent of the children showed clinical evidence of scoliosis and 6.4 per cent had positive radiological findings. Small curves were equally distributed between the two sexes, while large ones were more common in girls. Children with fair hair and blue eyes showed a higher percentage of positive findings than children with a dark complexion. A group of 112 children with curves between 7 and 16 degrees were followed up for an average of nineteen months. The pattern and evolution of these curves showed their close relationship to established scoliosis. Potential factors of instability and deterioration of the curves were evaluated.