Objective: To identify associations of maternal hemoglobin (Hb) with perinatal outcomes at low and moderate altitudes in Peru. Methods: Study of records with sequential information using perinatal database system. The study included 295 651 pregnant women with their products. Using multiple logistic regression analysis, we estimated the probability of stillbirths, preterm and small for gestational age (SGA) births associated with maternal Hb levels at low (01999 m) and moderate altitudes (20002999 m). Results: Maternal Hb decreased as pregnancy progressed from first to third trimester at both altitudes. Hb was higher at moderate than at low altitude (p<0.001). Risks for stillbirths increased with low maternal Hb (odds ratio [OR]: 1.39 for Hb 99.9; OR: 1.84 for Hb 88.9; OR: 3.25 for Hb 77.9; and OR: 7.8 for Hb <7g/dl); with Hb higher than 14.5g/dl (OR: 1.31) and with altitudes ≥2000 m (OR: 1.2). High preterm rates were also observed with low Hbs (OR: 1.16 for Hb 99.9; OR: 1.64 for Hb 88.9; OR: 2.25 for Hb 77.9; and OR:2.87 for Hb<7g/dl) and with Hb higher than 14.5g/dl (OR: 1.14). High SGA rates were observed in neonates with maternal Hb of 77.9 (OR: 1.35) and <7g/dl (OR:1.57), and higher than 14.5g/dl (OR: 1.33), and with moderate altitudes (OR: 1.12). The cut-off points for lower risks of stillbirth and preterm births was 10g/dl, and for SGA 9g/dl of hemoglobin. Conclusion: Low and high maternal Hb levels and moderate altitude were independent risk factors for adverse perinatal outcomes. © 2012 Informa UK, Ltd.