Medical issues can be misunderstood and mistreated as psychiatric disorders in individuals with developmental disabilities (DD). Inappropriate use of psychotropic medication may exacerbate unrecognized medical problems leading to additional medical and behavioural concerns. Individuals who may be most vulnerable to this are those with major communication impairments such as individuals with severe DD and/or autism. This paper describes a case of a 42-year-old man with a diagnosis of schizophrenia and severe DD who presented with severe aggression necessitating admission to a specialized dual diagnosis inpatient unit. Comprehensive inpatient assessment included medical assessment and behaviour monitoring and indicated a longstanding risk for bowel obstruction, clinical presentation consistent with autism, lack of clear evidence for the original diagnosis of schizophrenia, and sensitivity to psychotropic medications. Treatment involving simple nursing and behavioural interventions as well as discontinuation of all psychotropic medication proved very effective with NO incidence of aggression at seven-month follow up. Importance of nursing assessment/treatment combined with behaviour monitoring is emphasized.