A child with lobar holoprosencephaly presented with spastic diplegia and mild mental retardation, compounded by attention deficits and hyperactivity. His facial features were normal, and except for borderline microcephaly, there were no other predictors of holoprosencephaly. This patient represents the mild end of the spectrum of the holoprosencephaly malformation complex, which seems to be under-represented in the medical literature. Holoprosencephaly does not appear to have been described previously in association with spastic diplegia. This patient also illustrates the value of CT scans of the head of patients with neurological findings, without specific etiology.