To determine whether there was any difference in childhood leukemia incidence rates between populations living in the proximity to oil fields and those living in areas free from oil exploitation in the Amazon basin of Ecuador, 91 cancer cases among children (0–14 years) from the provinces of Sucumbios, Orellana, Napo, and Pastaza during the period 1985–2000 were studied. The relative risks for all leukemias indicated significantly elevated levels in the youngest age group (0–4 years), both genders combined (RR 3.48, 95% CI 1.25–9.67), and in all age groups (0–14 years) combined for females (RR 2.60, 95% CI 1.11–6.08) and both genders combined (RR 2.56,95% CI 1.35–4.86). There was no significant difference between the two groups in all other cancer sites combined. Study results are compatible with a relationship between childhood leukemia incidence and living in the proximity of oil fields in the Ecuadorian Amazon.