GADD45A is an evolutionary conserved gene whose expression is regulated by two major tumor suppressor proteins involved in breast cancer etiology, namely, p53 and BRCA1, and which acts primarily in the control of the G2/M cell-cycle transition, apoptosis, and DNA repair. Following genotoxic stress, the p53 protein activates GADD45A transcription, whereas in absence of DNA damage, BRCA1 represses GADD45A expression through interaction with the zinc finger protein ZNF350. Moreover, BRCA1 can activate GADD45A gene expression through interactions with transcription factors binding to the gene promoter. On the basis of the intricate network of interactions between GADD45A, p53, and BRCA1, and the fact that both BRCA1 or TP53 mutations are involved in breast cancer tumorigenesis, we undertook the characterization of the entire coding sequence, intron/exon boundaries, and p53- and ZNF350-binding sequences of this potential breast cancer susceptibility candidate gene in a sample set of 96 women affected with breast cancer from non-BRCA1 and BRCA2 French Canadian families with a high risk of breast cancer and 95 healthy controls from the same population. Although none of the 12 identified sequence variations show a significant difference in frequency between both sample sets, haplotype phasing and frequency estimations identified a common haplotype displaying a higher frequency among the control group. As the variants present on this particular haplotype are noncoding variants in either intron 2 or 3, this finding will have to be further investigated in larger cohorts and other populations. In this regard, our study also identified tagging single nucleotide polymorphisms (tSNPs), providing useful data for other large-scale association studies.