Objectives: The objective of this study was to evaluate the association between breastfeeding duration and child neurodevelopment based on the Polish Mother and Child Cohort Study. Material and Methods: The current analysis included 501 mother–child pairs. The analysis evaluating the association between the length of breastfeeding and child neurodevelopment considered the following variables: maternal age and body mass index, weight gain during pregnancy, parental level of education, marital status, socioeconomic status, child gender, birthweight, type of delivery, preterm delivery, pre- and postnatal exposure to tobacco constituents and child day care attendance. Psychomotor development was assessed in 1-year-olds on the Bayley Scales of Infant and Toddler Development. Results: The length of breastfeeding correlated positively with maternal age at delivery (ρ = 0.13), maternal and paternal level of education (ρ = 0.2 and ρ = 0.14 respectively), birthweight (ρ = 0.1) and marital status (ρ = 0.16) (p < 0.05). A negative correlation between the length of breastfeeding and maternal smoking status during the first year after delivery (ρ = –0.19) and weight gain during pregnancy (r = –0.1) was observed (p < 0.05). The association between the duration of breastfeeding and child development was not statistically significant in the model with the inclusion of confounding variables. A significant association between language development and maternal level of education (p = 0.004), gender of the child (p = 0.0007) and maternal weight gain during pregnancy (p = 0.01) was found. A negative association between cognitive development and maternal salivary cotinine during pregnancy (p = 0.03) and a negative association between motor development and maternal smoking status during the first year after delivery (p = 0.007) were also found. Conclusions: This study found no significant association between the duration of breastfeeding and child development after adjustment for confounders. Int J Occup Med Environ Health. 2019;32(2):175–84