Background Published data support the presence of etiologic heterogeneity by breast tumor subtype, but few studies have assessed this in Hispanic populations. Methods We assessed tumor subtype prevalence and associations between reproductive factors and tumor subtypes in 1041 women of Mexican descent enrolled in a case-only, binational breast cancer study. Multinomial logistic regression comparing human epidermal growth factor receptor 2 positive (HER2+) tumors and triple negative breast cancer (TNBC) to luminal A tumors was conducted. Results Compared to women with luminal A tumors, those with a later age at first pregnancy were less likely to have TNBC (odds ratio [OR], 0.61; 95% CI, 0.39–0.95), whereas those with ≥ 3 full-term pregnancies were more likely to have TNBC (OR, 1.68; 95% CI, 1.10–2.55). A lower odds of TNBC was shown for longer menstruation duration, whether prior to first pregnancy (OR, 0.78; 95% CI, 0.65–0.93 per 10 years) or menopause (OR, 0.79; 95% CI, 0.69–0.91 per 10 years). Patients who reported breastfeeding for >12 months were over twice as likely to have TNBC than luminal A tumors (OR, 2.14; 95% CI, 1.24–3.68). Associations comparing HER2+ to luminal A tumors were weak or non-existent except for the interval between last full-term pregnancy and breast cancer diagnosis. Conclusions Findings show etiologic heterogeneity by tumor subtype in a population of Hispanic women with unique reproductive profiles. Impact Identification of etiologically distinct breast tumor subtypes can further improve our understanding of the disease and help provide personalized prevention and treatment regimens.