Sever's injury (apophysitis calcanei) is considered to be the dominant cause of heel pain among children. Common advice is to reduce physical activity. However, our previous study showed that application of insoles reduced pain in Sever's injury without having to reduce physical activity. The purpose of this study was to test which of the two insoles, the heel wedge or the heel cup, provided best pain relief during sport activity in boys with Sever's injury (n=51). There was a crossover design in the first randomized part of the study. In the second part, the boys, 9–14 years, chose which insole they preferred. There was a reduction in odds score for pain to a fifth (a reduction of 80%) for the cup compared with the wedge (P<0.001). When an active choice was made, the heel cup was preferred by >75% of the boys. All boys maintained their high level of physical activity throughout. At 1-year follow-up, 22 boys still used an insole and 19 of them reported its effect on pain as excellent or good (n=41).