INTRODUCTION Low birth weight (LBW) is a major health problem and a significant contributor to neonatal death in both industrialised and developing countries. This study examined the prevalence and risk factors for LBW in Yazd, a central city of Iran. METHODS In this cross-sectional study, we evaluated all births that were registered in all the maternity hospitals in Yazd, Iran in 2008. LBW neonates were compared with neonates whose birth weight exceeded 2,500 g. RESULTS The overall prevalence of LBW was 8.8 percent. Univariate analysis using chi-square test showed that the risk factors associated with LBW were first and second pregnancies, teenage pregnancy, maternal diseases (pregnancy-induced hypertension, chronic hypertension and urinary tract infection), childbirth interval of less than three years, especially less than one year from the previous birth, preterm labour and working mothers. In multivariate analysis, preterm labour (odds ratio [OR] 5.2, 95 percent confidence interval [CI] 4.8-6.11), working mothers (OR 2.7, 95 percent CI 1.25-3.1) and pregnancy-induced hypertension (OR 1.5, 95 percent CI 1.2-2.22) were found to be risk factors for LBW. CONCLUSION Screening for high-risk pregnancies, such as teenage pregnancies and those with short birth intervals and maternal disease, as well as making provisions for attentive prenatal care and facilities are essential to reduce the incidence of LBW.