In the course of producing the 2009 NHS Evidence--skin disorders Annual Evidence Update on Acne Vulgaris, 25 randomised controlled trials were examined. From these, at least 12 potentially serious problems of trial reporting were identified. Several trials concluded no effect of a treatment yet they were insufficiently powered to exclude potentially useful benefits. There were examples of duplicate publication and "salami publication", as well as two trials being combined and reported as one. In some cases, an incorrect "within-groups" statistical comparison was made and one trial report omitted original efficacy data and included only P values. Both of the non-inferiority studies examined failed to pre-specify a non-inferiority margin. Trials reported as "double-blind" compared treatments that were dissimilar in appearance or had differing adverse effect profiles. In one case an intention-to-treat analysis was not performed and there was a failure to account for all of the randomized participants. Trial results were made to sound more impressive by selective outcome reporting, emphasizing the statistical significance of treatment effects that were clinically insignificant, and by the use of larger-sounding odds ratios rather than rate ratios for common events. Most of the reporting problems could have been avoided by use of the CONSORT guidelines and prospective trial registration on a public clinical trials database.