Short interpregnancy interval (IPI) is associated with low birth weight among Black and White women, but the effect of IPI on pregnancy outcomes in Latina women is unknown. The objective of this study was to measure the association between IPI and low birth weight among Mexican-origin Latina and White women. From the 1991 US birth certificate database, we selected singleton infants born to parous Mexican-origin Latina and White women, matching by month of infant birth and county of maternal residence(n=299,216). The dependent variables were very low (VLBW, 500-1,499 grams), moderately low (MLBW, 1,500-2,499 grams) and normal birth weight (2,500-4,000 grams, reference). The independent variable was interpregnancy interval, the number of months between the previous delivery and conception of the index pregnancy: <6, 6-11, 12-17, 18-23, 24-35 (reference) and >35 months. Logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (CI) for the risk of IPI on low birth weight. Nine percent of women had a short IPI (<6 months) and 37% had a long IPI (>35 months). Women with short and long IPI were more likely to be Latinas, had less education, higher parity, and higher rates of tobacco use than women with intermediate IPI. After adjusting for maternal ethnicity, age, education, birthplace, parity, tobacco use, obstetric and medical complications, utilization of prenatal care, and infant sex, women with a short IPI were 43 to 71 percent more likely to have VLBW (OR 1.71, CI 1.25-2.33) and MLBW infants (OR 1.43, CI 1.26-1.62) than women with an intermediate IPI. Women with a long IPI were 30 percent more likely to have VLBW (OR 1.30, CI 1.01-1.66) and MLBW infants (OR 1.27, CI 1.15-1.41) than women with an intermediate IPI. After controlling for numerous risk factors, both short and long interpregnancy intervals were associated with an increased risk of very low and moderately low birth weight infants among Mexican-origin Latina and White women. Further study is needed to identify the social and biological factors associated with interpregnancy interval, and the mechanisms through which interpregnancy intervals influence pregnancy outcomes.