We report the case of a young patient with macrocephaly. After excluding the most frequent causes of macrocephaly (hereditary disorders, degenerative, osseous and metabolic diseases, neurocutaneous syndromes and cerebral malformations), the likelihood of a chromosome disorder was investigated, revealing an unbalanced de novo translocation: 46,X,der(X),t(X;7) (q13 or q13.2; q11.23 or q21.11), i.e., a partial trisomy of the long arm of chromosome 7, associated with a partial monosomy of the long arm of chromosome X. Though this chromosome disorder is relatively rare, it should be considered in the differential diagnosis of patients under one year of age presenting with macrocephaly, scoliosis and non-progressive psychomotor retardation.