Background: Intrusive interventions, once implemented, may remain in place longer than necessary unless their continued effectiveness is evaluated. Method: We conducted a phased timeout-evaluation for 34 individuals with developmental disabilities who received services from the same agency and whose treatment programmes contained timeout for aggression and/or property destruction. After establishing baseline rates of problem behaviour (with timeout in effect), we removed timeout from all programmes through a gradual process that occurred over a 1-year period. Results: Rates of problem behaviour decreased (or did not increase) for 21 individuals following the removal of timeout. Rates of problem behaviour increased for 13 individuals, but alternative procedures that were less intrusive than timeout were implemented for 10 individuals. Timeout was reinstated for the remaining three individuals and was associated with reductions in problem behaviour. Conclusions: The phased timeout evaluation resulted in successful removal of 91% (31 of 34) of the original timeout programmes.