Useful clinician-rated measures of OCD are now available. The Y-BOCS and NIMH Global OC both seem suitable for monitoring outcome in drug trials of OCD. These two scales seem relatively specific for symptoms of OCD and are sensitive to drug-induced changes in symptoms. Neither the Y-BOCS nor the NIMH Global OC confuse trait with state. There are ample data suggesting that the Y-BOCS is reliable and valid scale. Unlike some of the symptom inventories, such as the LOI and MOCI, final scores on the NIMH Global OC and Y-BOCS are not influenced directly by the type or number of obsessions and compulsions present. A computer-administered version of the Y-BOCS has been developed. Currently available patient-rated instruments suffer from serious shortcomings, including insensitivity to change and poor representation of patients with mono-symptomatic clinical pictures (e.g., hoarding alone). Some rating scales have been adapted for use in children with OCD. Several groups, including our own, have elected to use change scores on the 10-item Y-BOCS and a global measure of OCD, such as the NIMH Global OC or modified OGI, as the principal outcome variables in drug trials in patients with OCD. Several studies have selected a 35% decrease in Y-BOCS scores from baseline as indicative of clinically significant improvement. A limitation of all single-item global measures is that they cannot be resolved into smaller components. The more fine-grained analysis that is possible with the multi-item Y-BOCS makes it more desirable as a primary outcome measure, with a global scale as a secondary outcome measure.