The authors examined whether D-cycloserine, a partial agonist at the glutamatergic N-methyl-d-aspartate receptor, augments and accelerates a full course of comprehensive cognitive-behavioral therapy (CBT) in adults with generalized social anxiety disorder. This was a multisite randomized placebo-controlled efficacy study with 169 medication-free adults with generalized social anxiety disorder, of whom 144 completed the 12-week treatment and 131 completed the three follow-up assessments. Patients were randomly assigned to receive 50 mg of D-cycloserine or placebo 1 hour before each of five exposure sessions that were part of a 12-session cognitive-behavioral group treatment. Response and remission status was determined at baseline, throughout treatment, at end of treatment, and at 1-, 3-, and 6-month follow-up assessments by assessors who were blind to treatment condition. D-Cycloserine-augmented and placebo-augmented CBT were associated with similar completion rates (87% and 82%), response rates (79.3% and 73.3%), and remission rates (34.5% and 24.4%) at the posttreatment assessment; response and remission rates were largely maintained at the follow-up assessments. Although D-cycloserine was associated with a 24%-33% faster rate of improvement in symptom severity and remission rates relative to placebo during the treatment phase, the groups did not differ in response and remission rates. D-Cycloserine did not augment a full course of comprehensive CBT for social anxiety disorder.