Purpose -The purpose of this paper is to describe the characteristics of adult male autistic spectrum disorder (ASD) patients admitted to low secure services and to compare them with non-ASD patients. Design/methodology/approach -Case-control study of admissions to two ASD units and one non-ASD unit at a tertiary referral centre. Subjects were compared on demographic, personal, clinical and offending behaviour variables. Findings -In total, 51 ASD and 43 controls were studied. Median age at diagnosis of ASD was 21 years (range 6-56). The ASD group were younger (median age 27 vs 33 years) and more likely to be single than controls. Their age at first contact with psychiatric services was lower and proportionally more were admitted from prison and courts. Almost three-quarters had psychiatric comorbidity, most commonly schizophrenia, but unlike controls, personality disorder and drug and alcohol disorders were uncommon. Lifetime sexually inappropriate behaviour and physical violence were less common, as was non-compliance with medication. However, 78 per cent had a lifetime history of physical violence and a third had a conviction for GBH or homicide. Offending behaviour was sometimes atypical in nature and some had convictions for unusual offences such as harassment and stalking.Research limitations/implications -The age difference between cases and controls is likely to have confounded the results. Findings cannot be generalised to the NHS. Originality/value -This group of ASD patients in low security differed in several important respects from their non-ASD counterparts, which highlights their differing treatment needs, strengths and weaknesses.