Two families and three sporadic cases have been described so far with the combination of radio-ulnar synostosis and microcephaly as main features. Some authors have discussed whether the first family reported by Giuffrè et al. [1994] and the second family described by Tsukahara et al. [1995] had the same syndrome. Although there is phenotypic variability among the described cases (especially with respect to facial dysmorphisms and mental retardation), the clinical patterns do not seem to be clearly distinguishable from each other. We describe another family with apparent X-linked semi-dominant inheritance with milder features in the female patient due to skewed X-inactivation. From a clinical synopsis, we consider the Giuffrè-Tsukahara syndrome as one genetic entity, which is characterized by the association of microcephaly and radio-ulnar synostosis, mental retardation in male patients and variable minor features. Patients with the Giuffrè-Tsukahara syndrome do not present with a characteristic pattern of facial features.