Objective: To determine hemoglobin values associated with adverse maternal outcomes among Peruvian populations at different altitudes. Methods: A retrospective cohort study was conducted using data from the Perinatal Information System. Adverse maternal outcomes were assessed. Results: Risk of pre-eclampsia increased at maternal hemoglobin levels above 14.5 g/dL (OR 1.27; 95% CI, 1.18-1.36) or below 7.0 g/dL (OR 1.52; CI 95%, 1.08-2.14). Altitude above 2000 m reduced risk (OR 0.65; 95% CI 0.62-0.68). Risk of postpartum hemorrhage (PPH) increased with moderate/severe anemia (OR 6.15; 95% CI, 3.86-9.78) and at moderate altitudes (OR 1.26; 95% CI, 1.12-1.43). Mild anemia at any altitude was associated with reduced risk of pre-eclampsia (OR 0.85, 95% CI, 0.81-0.89) and PPH (OR 1.01; 95% CI, 0.88-1.15). Risk of premature rupture of membranes was reduced at high hemoglobin values. Maternal mortality increased at hemoglobin levels below 9.0 g/dL (OR 5.68; 95% CI, 2.97-10.80) and above 14.5 g/dL (OR 2.18; 95% CI, 1.22-3.91). Maternal mortality increased at moderate altitudes (OR 29.2; 95% CI, 2.62-324.60) and high altitudes (OR 66.4; 95% CI, 6.65-780.30) when hemoglobin levels were below 9.0 g/dL. Conclusion: Elevated altitude and hemoglobin levels influence maternal outcomes. © 2012 International Federation of Gynecology and Obstetrics.