To study the genetics of asthma, a familial collection was built in the Saguenay-Lac-Saint-Jean (SLSJ) region, which is localized in northeastern Quebec, Canada, and which is characterized by a young founder effect. Recruitment was performed through probands with a specific asthma phenotype. The collection includes 1394 individuals distributed in 271 families. A phenotypic profile including more than 75 phenotypic characteristics was defined for each participant using a standardized questionnaire, respiratory measures and allergic tests. A genome-wide association study on 1214 of these samples for asthma-related phenotypes (asthma, atopy and rhinitis) and for white blood cell types was performed. These analyses allowed associating 10 single nucleotide polymorphisms (SNPs) with P<1 × 10(-5) with asthma-related phenotypes and 11 SNPs with white blood cell counts. Among them, four SNPs are located in or near genes with functions related to asthma or allergy. Moreover, several loci were identified as 5q31.1 that includes 22 SNPs associated with atopy (P<1 × 10(-3)) and located near a cytokine cluster, and 17q21.2 with seven SNPs associated with asthma. This study highlights the value of a familial collection with a fine phenotypic description and characterized by a young founder effect in the search of the genetic determinants involved in complex traits such as asthma.