Hereditary hypotrichosis simplex (HHS) is a form of nonsyndromic inherited hair loss disorders without characteristic hair shaft changes, which has marked genetic and clinical heterogeneity. After mapping the locus to 13q12.12–12.3 in a Chinese family with a generalized variant of autosomal dominant HHS (ADHHS), exome sequencing was performed in an affected individual. The cause of the disease in this family was identified as a c.95G>A (p.Arg32Gln) mutation in the RPL21 gene, which encoding the ribosomal protein L21. This mutation cosegregated completely with the disease phenotype and was not observed in unaffected family members, 200 normal controls, the dbSNP database, the YH database or pilot data from the 1000 Genomes Project. Additionally, this mutation was found in two patients from another unrelated Chinese family with HHS. To the best of our knowledge, this is the first report describing the involvement of a ribosomal protein gene mutation in a non-syndromic hair loss disorder. Hum Mutat 32:1–5, 2011. © 2011 Wiley-Liss, Inc.