Background: Allergic diseases are thought to be inherited. Prevalence of allergic diseases has, however, increased dramatically in last decades, suggesting environmental causes for the development of allergic diseases. Objective: We studied risk factors associated with the development of atopic dermatitis (AD), allergic rhinitis (AR) and asthma (AS) in children of non-atopic parents in a subtropical country. Methods: In a birth cohort of 1,497 newborns, parents were prenatally enrolled and validated for allergic diseases by questionnaire, physician-verified and total or specific Immunoglobulin E (IgE) levels; 1,236 and 756 children, respectively, completed their 3-year and 6-year follow-up. Clinical examination, questionnaire, and blood samples for total and specific IgE of the children were collected at each follow-up visit. Results: Prevalence of AD, AR and AS was, respectively, 8.2%, 30.8% and 12.4% in children of non-atopic parents. Prevalence of AR (p<. 001) and AS (p=. 018) was significantly higher in children of parents who were both atopic. A combination of Cesarean section (C/S) and breastfeeding for more than 1 month showed the highest risk for AD (OR= 3.111, p=. 006). Infants living in homes with curtains and no air filters had the highest risk for AR (OR= 2.647, p<. 001), and male infants of non-atopic parents living in homes without air filters had the highest risk for AS (OR= 1.930, p=. 039). Conclusions: Breastfeeding and C/S affect development of AD. Gender, use of curtains and/or air filters affect AR and AS, suggesting that control of the perinatal environment is necessary for the prevention of atopic diseases in children of nonatopic parents.