OBJECTIVE: To examine the risk of preterm birth (PTB) in relation to maternal psychiatric symptoms during pregnancy in Peruvian women. STUDY DESIGN: This case-control study included 479 PTB cases and 480 term controls. In-person interviews were conducted to assess women's depressive, anxiety, and stress symptoms using the Patient Health Questionnaire (PHQ-9) and the Depression Anxiety Stress Scales (DASS-21). Multivariable logistic regression procedures were used to estimate adjusted odds ratios (aORs) and 95% confidence intervals (CIs). RESULTS: Compared with women reporting no or minimal depressive symptoms, the aOR (95% CI) for PTB associated with consecutive severity of depressive symptoms based on the PHQ-9 assessment method were as follows: mild, 2.22 (95% CI 1.64-3.00) and moderatesevere, 3.67 (95% CI 2.09-6.46). The corresponding aORs for normal, mild, and moderate-severe depressive symptoms based on the DASS-21 assessment were 1.00 (reference), 3.82 (95% CI 1.90-7.66), and 2.90 (95% CI 1.66-5.04), respectively. A positive gradient was observed for the odds of PTB with severity of anxiety (ptrend <0.001) and stress symptoms (ptrend <0.001). CONCLUSION: The odds of PTB increased in pregnant Peruvian women with psychiatric symptoms. Efforts to screen and treat affected women may modify risks of PTB and possibly other associated disorders. © Journal of Reproductive Medicine®, Inc.