A boy with classical Rubinstein-Taybi syndrome but no detectable mutation in the CREBBP and EP300 genes: Rubinstein-Taybi syndrome (RTS) is a rare autosomal dominant genetic disorder and is characterized by mental retardation, distinctive facial features, broad and often angulated thumbs and great toes. We report on a 7 year old boy with classical Rubinstein-Taybi syndrome. His facial and clinical features were very typical, including broad thumbs with radial angulation and broad great toes. Rigorous genetic analysis of the CREBBP and EP300 genes using DNA sequencing and multiple ligation-dependent probe amplification (MLPA) revealed no causative mutation in this boy, only a hitherto unreported but paternally inherited heterozygous sequence alteration, c.5061 + 9C>T in IVS 30-31, which most likely represents a normal variant (NetGene 2 splice prediction software). We question if this boy could have a hitherto undetectable mutation type.