ABSTRACTThe hypothesis of this study was to determine whether the use of rectal diazepam in solution would effectively modify the uncooperative behavior of patients with mentally and physically handicapping conditions during dental treatment. The sample consisted of 42 patients with mild to severe mentally handicapping conditions, 4 to 31 years old, who live in a homecare center. Supragingival and subgingival scaling and prophylaxis were attempted during a 5‐minute period and the patient's behavior was assessed. Conscious sedation using a rectal solution of diazepam (Stesolid) was used for those patients with voluntary or involuntary uncooperative behavior that prevented treatment. Twenty‐two subjects (52.4%) were treated without diazepam. The rectal solution of diazepam proved to be a significantly (P<.01) effective agent for behavior modification permitting the successful treatment of 16 (80%) of the 20 remaining subjects. The following behaviors were significantly modified: places hand(s) or arm(s) in front of mouth (P<.01); does not open mouth, lips held firmly together (P<05); turns head to one side or side to side (P<05); attempts to grab instruments (P<.05). No relationship was found between the results and the variables of medical history, gender, age, weight, quantity of diazepam administered, routine medication, pulse rate, blood pressure, and respirat