Purpose of the Study. To investigate the effect of vaccination with BCG on the development of atopic diseases in a homogeneous population of Spanish schoolchildren. Study Population. Children aged 6 to 7 years who were living in 3 cities (Bilbao, San Sebastian, and La Coruna) and 1 province (Asturias) of the North Atlantic coast of Spain. Methods. The International Study of Asthma and Allergies in Childhood (ISAAC) core and environmental questionnaires were used in 4 different centers of the Spanish North Atlantic coast. Bilbao, San Sebastian, and Asturias have a universal BCG immunization policy during the first days of life, whereas La Coruna discontinued this practice in 1989. Except for this center, immunization coverage was >90%. Parents of children aged 6 and 7 years were surveyed from a random sample of schools of Asturias or all schools in the city district among the remainder of the centers. Results. The participation rate was >70%. After excluding those children born outside Spain, there were 6762 immunized and 2828 nonimmunized. After adjusting for gender, age, smoking habits of the father and mother, truck traffic near the household, presence of older and younger siblings, and ownership of a cat or a dog during the first year of the child’s life, the adjusted odds ratios of the BCG-immunized children according to disease outcome were 0.87 for asthma (95% confidence interval [CI]: 0.76–1.00), 0.87 for hay fever (95% CI: 0.75–1.01), and 0.89 for atopic dermatitis (95% CI: 0.76–1.05). Conclusions. BCG immunization offers weak protection against atopic diseases in Spanish schoolchildren. Reviewer Comments. BCG vaccination has received attention because of its ability to provoke a T-helper (Th)1 response. Many investigators have hypothesized that vaccination with BCG may offer protection from Th2-skewed diseases such as asthma, allergic rhinitis, and atopic dermatitis. Although this study reveals that immunization with BCG offers weak protection against asthma and allergic rhinitis in a homogeneous population, it is important to remember that these diseases are multifactorial, with genetic and environmental influences also impacting pathogenesis.