OBJECTIVE: To examine risk factors for pregnancy among adolescent girls in the Amazon basin of Ecuador. METHODS: A matched case-control study with cases and controls identified within a community-based demographic and health survey was conducted in Orellana, Ecuador, from May to November 2006. A questionnaire focused on socioeconomic status, family structure, education, reproductive health, and childhood-adolescent trauma was applied. Conditional logistic regression was used to adjust for potential confounders. RESULTS: Respondents included 140 cases and 262 controls. Factors associated with increased risk of adolescent pregnancies through multivariate analysis were: sexual abuse during childhood-adolescence (odds ratio (OR) 3.06, 95% confidence interval (CI) 1.08-8.68); early sexual debut (OR 8.51, 95% CI 1.12-64.90); experiencing periods without mother and father (OR 10.67, 95% CI 2.67-42.63); and living in a very poor household (OR 15.23, 95% CI 1.43-162.45). Another two factors were statistically associated in the bivariate analysis: being married or in a consensual union (OR 44.34, 95% CI 17.85-142.16) and not being enrolled in school at the time of the interview (OR 6.31, 95% CI 3.70-11.27). For a subsample of sexually initiated adolescents, "non-use of contraception during first sexual intercourse" was also found to be a risk factor (OR 4.30, 95% CI 1.33-13.90). CONCLUSION: The study found that early sexual debut, non-use of contraception during first sexual intercourse, living in a very poor household, having suffered from sexual abuse during childhood-adolescence, and family disruption (living extended periods of life without both parents) were associated with adolescent pregnancy in Orellana.