ThePOU1F1gene encodes a transcription factor that is important for the development and differentiation of the cells producing GH, prolactin, and TSH in the anterior pituitary gland. Patients withPOU1F1mutations show a combined pituitary hormone deficiency with low or absent levels of GH, prolactin, and TSH. Fourteen mutations have been reported in thePOU1F1gene up to now. These genetic lesions can be inherited either in an autosomal dominant or an autosomal recessive mode. We report on the first Italian patient, a girl, affected by combined pituitary hormone deficiency. The patient was found to be positive for congenital hypothyroidism (with low TSH levels) at neonatal screening. Substitutive therapy was started, but subsequent growth was very poor, although psychomotor development was substantially normal. Hospitalized at 10 mo she showed hypotonic crises, growth retardation, delayed bone age, and facial dysmorphism. In addition to congenital hypothyroidism, GH and prolactin deficiencies were found. Mutation DNA analysis of the patient’sPOU1F1gene identified the novel Q167K amino acid change at the heterozygous level. The highly conserved Q167 residue is located in thePOU-specific domain. No mutation was detected in the other allele. DNA analysis in the proband’s parents did not identify this amino acid substitution, suggesting ade novogenetic lesion. From these data it can be hypothesized that the Q167K mutation has a dominant negative effect.