Studies have consistently identified a positive association between prenatal weight gain and birth weight. Much less, however, is known about factors that may influence women to gain weight within currently recommended ranges. The importance of this issue is suggested by recent reports indicating that only 30-40% of women actually gain weight within these ranges. This paper examines demographic, sociocultural, and behavioral factors that are associated with, and may influence risk of, low prenatal weight gain among adult women with low and normal body mass indexes. Available data suggest that these factors include ethnicity, socioeconomic status, age, education, pregnancy intendedness or wantedness, prenatal advice, and psychosocial characteristics such as attitude toward weight gain, social support, depression, stress, anxiety, and self-efficacy. Potential theoretical models for these associations include biological, behavioral, and mixed pathways. The design of targeted intervention studies will depend on further identification and characterization of sociocultural and behavioral risk factors that, along with reproductive and nutritional characteristics, may predict which women are most likely to have inadequate prenatal weight gain.