BACKGROUND It is reported that people with mild learning disability have a higher point prevalence of schizophrenia than the normal population, the reasons for which are unclear.

METHOD Thirty-nine subjects with mild learning disability and schizophrenia, 34 control subjects with schizophrenia and 28 control subjects with mild learning disability were seen. Interviews with relatives and carers were also conducted. Assessments were made of clinical variables, psychopathology, neurological 'soft' signs, IQ, memory and family history. Blood was taken for karyotypic analysis from comorbid subjects.

RESULTS The comorbid group had more negative symptoms, episodic memory deficits, soft neurological signs, epilepsy and receive more community supports than control subjects with schizophrenia. Comorbid subjects had a tendency to belong to multiply affected families and show high rates of chromosomal variants on routine karyotypic testing.

CONCLUSIONS Future work on the generality of schizophrenia should include people with premorbid learning disability, as a discrete subtype from whom valuable genetic aetiological clues may be obtained.