This preprint reports a double-blind, randomized clinical trial of 62 patients to assess the efficacy of hydroxychloroquine (HCQ) in mild COVID-19. Patients in the treatment arm received 400 mg HCQ per day for 5 days. Fever and cough resolved on average 1 day earlier with HCQ, although the distribution of symptomatic patients at day 0 was not even between groups. No patients receiving HCQ progressed to severe disease, whereas 4 of 31 patients in the control arm progressed. Few clinical data and no viral load measurements were reported, limiting the conclusions that can be drawn from this trial. This study suggests relative efficacy for patients with mild disease and warrants larger clinical trials, but the effects of HCQ on patients with more severe COVID-19 remain unknown.