There has been a long-running controversy about the relative benefits of Assertive Community Treatment (ACT) compared to Case Management (CM). Several health care systems have initiated major service overhauls on the basis of published evidence. Yet this evidence has been ambiguous and supports differing interpretations. Research is examined which explores the differences in outcomes reported. It uses a range of approaches, most prominently meta-regression, to test a small range of hypotheses to explain the heterogeneity in outcomes. The main determinant of differences between ACT and CM studies is the local bed management procedures and occupancy practice. Those organizational aspects of ACT which are generally shared by CM teams are associated with reduced hospital care but the stringent staffing proposed for ACT does not affect it. ACT is a specialized form of CM, not a categorically different approach. The benefits of introducing it will depend on the nature of current local practice. Important lessons about the need to focus on treatments rather than structures seem not to have been learnt. Psychiatry's recent excessive focus on service structures may have had unintended consequences for our professional identity.