Objective: This study evaluated the adequacy of pharmacological antidepressant treatment in major depressive episodes prescribed in 16 Spanish primary care centers, both during the acute phase of treatment and after the first three months of the continuation phase, under real-world naturalistic conditions (usual care). Factors that could be associated with adequacy of care also were explored. Methods: A total of 333 patients from primary care who began pharmacological antidepressant treatment were followed up for six months. Treatment adequacy and associated factors were evaluated. Results: Between 27% and 32% of patients received adequate antidepressant treatment during the acute phase. Percentages of adequacy were between 21% and 25% when considering the acute phase and the first three months of the continuation phase. Psychiatric consultations were found to be associated with treatment adequacy. Conclusions: In state-funded Spanish primary care centers, antidepressant treatment adequacy was poor during both the acute phase and the first three months of the continuation phase. Primary care physicians prescribed suggested antidepressants, mostly as recommended (99%) and at adequate dosages. However, they did not perform the recommended number of follow-up sessions and treated patients with depressive disorders other than major depression as if they had a major depressive episode. Collaborative interventions between primary and specialized care could improve treatment adequacy.