OBJECTIVE: To compare morbidity and mortality rates of low birth weight (LBW) and appropriate birth weight infants born at term, focusing on diarrheal and respiratory infections. STUDY DESIGN: A cohort of 133 LBW infants (1500 to 2499 gm) and 260 appropriate birth weight infants (3000 to 3499 gm), individually matched by sex and season of birth, were followed for the first 6 months of life. None had congenital anomalies and all were from poor families living in the interior of Pernambuco, northeast Brazil. Data on infant deaths, hospitalizations, and morbidity were collected prospectively through daily home visits (except Sundays) from birth through week 8, then twice weekly for weeks 9 to 26. The effects of birth weight were assessed with a variety of multivariable techniques, controlling for confounders. RESULTS: Of the LBW infants, 56% were wasted (thin), 23% were stunted, and 17% were both wasted and stunted. The LBW infants (median 2380 gm) experienced a sevenfold higher mortality rate and fourfold higher rate of hospitalization than appropriate birth weight infants. Almost all deaths and hospitalizations were in the postneonatal period. The LBW infants also experienced 33% more days with diarrhea and 32% more days with vomiting (p = 0.003 in each case). The prevalences of cough and fever were not significantly different. CONCLUSIONS: Infant deaths, hospitalizations, and diarrheal morbidity are increased in term LBW infants who have only a modest weight deficit. (J PEDIATR 1996;128:497-504)