To examine the effects of socioeconomic status and biocultural variables (planned pregnancy, prenatal care, timing of initiation of breast-feeding and caesarean section delivery) on breast-feeding duration in Peru using structural equation models.

Structural equation models were analysed with LISREL using data from the 1991–92 Peruvian Demographic and Health Survey.

Models were tested among 6020 women whose last child was born within 5 years of the survey and among 2711 women whose last child was born 2–5 years preceding the survey.

Unplanned pregnancy and socioeconomic status had a negative influence on breast-feeding duration. Prenatal care was positively associated with the timing of breast-feeding initiation in both samples and with breast-feeding duration in the whole sample. The timing of breast-feeding initiation was inversely associated with breast-feeding duration only in the sample of older children.

These results imply that an unplanned pregnancy, a delayed breast-feeding initiation, and higher socioeconomic status are risk factors for an earlier discontinuation of breast-feeding through complex mechanisms involving direct and indirect effects.