Acne vulgaris has been postulated to have a gastrointestinal mechanism; however, little is known about gut microbiota dysfunction in this condition. The aim of this cross-sectional study was to investigate whether the gut microbiota is altered in acne. Faecal bacterial diversity was analysed in 43 patients with acne and 43 controls, using hypervariable tag sequencing of the V3-V4 region of the 16S rDNA gene. Distinct differences were found in microbial diversity between patients with acne and controls (Shannon diversity index (p = 0.009) and Simpson diversity index (p = 0.01)). At the phylum level, the abundance of Firmicutes was lower in the patient group, but that of Bacteroidiain was higher. The most significantly depleted taxa in acne were Clostridia, Clostridiales, Lachnospiraceae and Ruminococcaceae genera, which are potentially beneficial. In conclusion, patients with acne vulgaris have gut microbial dysbiosis; further study is needed to understand its role in the pathogenesis of acne.