Previous data suggested an association of vertebral anomalies with Wilms tumor. At the same time, vertebral midline fusion defects are often indicated by dermal anomalies over the spine. In the present study the prevalence of both occult spina bifida and cutaneous signs of spinal dysraphism was significantly higher in 50 Wilms patients than in 180 control children (18.0 versus 4.4%, p <.01, and 35.9 versus 17.5%, p <.02, respectively). Family investigations are needed to answer the question whether signs of spinal dysraphism in parents and sibs of patients may be regarded as indicators of an increased risk of Wilms tumor in the family.