Aims: To determine the prevalence of physical illness in patients admitted to a challenging behaviour unit and to assess whether they were physically examined and investigated.Method: Retrospective case note analysis of patients admitted to the challenging behaviour unit during the period of July 1997 to July 2003.Results: All patients were suffering from serious and enduring mental illness and challenged the ordinary mental health services by behaviour such as assault, fire setting, aggression, self harm, multiple substance misuse and non-compliance at least for six months.On admission 76% of patients had examination of the cardiovascular, respiratory and gastro intestinal system and 69% of the central nervous system. During the hospital stay, all the patients had cardio vascular, respiratory and gastrointestinal system examination and 83% had central nervous system examination. All patients had base line investigations including full blood count, ESR, liver function test, urea and electrolytes, random glucose, thyroid function test and follow up investigations.51(73%) patients were found to be suffering from some physical illness during their hospital stay. The physical illness spanned all the systems. There were newly detected cases of systemic lupus erythematosus, diabetes mellitus, glaucoma, hypertension, seizure disorder, male urinary tract infection, severe incontinence and haematological problems.Conclusion: There is a high prevalence of physical health problems among patients admitted to a challenging behaviour unit. Some problems were associated with the mental illness, some as a complication of the mental health problem and others secondary to psychotropic medication. This study highlights the importance of a proper medical history, physical examination, base line investigations and regular monitoring of the physical health of mentally ill patients.