PURPOSE: Plantar fasciitis is a very common (lifetime incidence ~ 10%) and long-lasting injury with major impact on daily function. Combining corticosteroid injection and physical training (strength training and stretching) was hypothesized to result in a superior effect compared to each treatment separately. METHODS: A single blinded randomized controlled superiority trial conducted in 2013-2014 with a 2-year follow-up (end Sept 2016). 123 consecutive patients (20-65 years) referred to two study centers in Denmark: Institute of Sports Medicine, Bispebjerg Hospital, University of Copenhagen and a private rheumatology clinic with symptoms of plantar fasciitis, and ultrasound measured thickness above 4.0 mm were invited. 25 did not fulfill the inclusion criteria (mainly ultrasound criteria) and 8 refused participation. 90 patients were randomized (pulling sealed envelopes) to 3 groups: (1) 3 months strength training and stretching (n = 30), (2) corticosteroid injections with monthly intervals until thickness < 4.0 mm (maximum 3 injections) (n = 31), (3) combination of the two treatments (n = 29). During the 3 months intervention period load reduction was recommended (cushioning shoes and insoles and abstaining from running and jumping). The main outcome was improvement in Pain at function on a 100-mm VAS score and in Foot Function Index (FFI, range 0-230) at 6 months (Clinicaltrials.gov Identifier: NCT01994759). RESULTS: All groups improved significantly over time, but the combination of corticosteroid injection and training (strength training and stretching) had a superior effect at all time points. The mean difference between the combined treatment and training was 40 points in FFI (95% confidence interval (CI) 63-17 points, p < 0.001) and 20 mm for VAS function pain (CI 35-5 mm, p < 0.01). The mean difference between the combined treatment and corticosteroid injections only was 29 points in FFI (CI 52-7 points, p < 0.01) and 17 mm for VAS function pain (CI 32-2 mm, p < 0.05). All differences were clinically relevant. CONCLUSION: The best treatment for plantar fasciitis is the combination of corticosteroid injections and training (strength training and stretching). This combined treatment is superior both in the short- and in the longterm. Corticosteroid injections combined with controlled training are recommended as first line treatment in patients with plantar fasciitis. LEVEL OF EVIDENCE: 1.