Plantar fasciitis is one of the most common foot complaints. It is often treated with foot orthoses; however, studies of the effects of orthoses are generally of poor quality, and to our knowledge, no trials have investigated long-term effectiveness. The aim of this trial was to evaluate the short- and long-term effectiveness of foot orthoses in the treatment of plantar fasciitis. A pragmatic, participant-blinded, randomized trial was conducted from April 1999 to July 2001. The duration of follow-up for each participant was 12 months. One hundred and thirty-five participants with plantar fasciitis from the local community were recruited to a university-based clinic and were randomly allocated to receive a sham orthosis (soft, thin foam), a prefabricated orthosis (firm foam), or a customized orthosis (semirigid plastic). After 3 months of treatment, estimates of effects on pain and function favored the prefabricated and customized orthoses over the sham orthoses, although only the effects on function were statistically significant. Compared with sham orthoses, the mean pain score (scale, 0-100) was 8.7 points better for the prefabricated orthoses (95% confidence interval, -0.1 to 17.6; P = .05) and 7.4 points better for the customized orthoses (95% confidence interval, -1.4 to 16.2; P = .10). Compared with sham orthoses, the mean function score (scale, 0-100) was 8.4 points better for the prefabricated orthoses (95% confidence interval, 1.0-15.8; P = .03) and 7.5 points better for the customized orthoses (95% confidence interval, 0.3-14.7; P = .04). There were no significant effects on primary outcomes at the 12-month review. Foot orthoses produce small short-term benefits in function and may also produce small reductions in pain for people with plantar fasciitis, but they do not have long-term beneficial effects compared with a sham device. The customized and prefabricated orthoses used in this trial have similar effectiveness in the treatment of plantar fasciitis.