Idiopathic scoliosis (IS) is a spine disorder of unknown origin with 1.5–3% prevalence in the general population. Besides the large multifactorial-form sample of IS, there is a good evidence for the existence of a monogenic subgroup in which the disease is inherited in a dominant manner. However, results from literature suggest a strong heterogeneity in the locations of the mutated genes. Using a high-resolution genome-wide scan, we performed linkage analyses in three large multigenerational IS families compatible with dominant inheritance including 9–12 affected members or obligate carriers. In two of these families, our results suggested intra-familial genetic heterogeneity, whereas, in the other, we observed a perfect marker disease co-segregation in two regions at 3q12. 1 and 5q13. 3. We can state that one of these two locations is a novel IS disease gene locus, as the probability of having this perfect co-segregation twice by chance in the genome is very low (P= 0.001). Lastly, in all three families studied, linkage to the previously mapped dominant IS loci on chromosomes 19p13. 3, 17p11. 2, 9q34, 17q25 and 18q is unlikely, confirming that there is a high genetic heterogeneity within the subgroup of dominant forms of IS.