Generalized anxiety disorder (GAD) is a chronic and disabling condition. The aim of this study was to evaluate the effectiveness of low-dose augmentative quetiapine (mean dose=50 mg/day) in patients with GAD and partial/no response to selective serotonin reuptake inhibitors (SSRIs). Twenty patients with GAD and partial/no response to SSRIs were randomized to quetiapine (n=10) or placebo (n=10) for 8 weeks, continuing their treatment with SSRIs. Analyses of variance with repeated measures on Hamilton Anxiety Rating Scale (HAM-A) and Clinical Global Impression (CGIs; severity of illness) were carried out at baseline and after 8 weeks and the number of responders/remitters was computed and compared between the groups. HAM-A scores at baseline were 15.60 (±4.48) in the placebo group and 18.50 (±6.59) in the quetiapine group, and at the end-point, HAM-A scores in the placebo group were 10.40 (±4.88) and 9.20 (±5.86) in the quetiapine group. A significant time-by-treatment effect was found on the HAM-A (F=5.19, P=0.035) and CGIs scores (F=19.60, P<0.001) in favor of the quetiapine group. The number of responders was numerically superior in the quetiapine group (60 vs. 30%) without reaching statistical significance (χ2=1.82, degree of freedom=1, P=0.37, φ=0.30). Remitters were 40% for the quetiapine group versus 20% for the placebo group (χ2=0.95, degree of freedom=1, P=0.63, φ=0.22). Low-dose augmentative quetiapine may be an useful treatment option for patients with GAD and partial/no response to SSRIs. The lack of double-blind conditions and the limited sample size may limit the confidence in the reported results. Larger randomized controlled trials are warranted to confirm these data.