Joubert syndrome co-existing with partial Xp trisomy. review of the literature: We report a five-year-old girl who has been clinically diagnosed as Joubert syndrome. Her cytogenetic analysis showed 46,XX,der(2)add(2q37) karyotype. Cytogenetic analysis of her mother and maternal grandmother revealed a karyogram designated as 46,X,t (X;2)(p11.2;q37). The proband's derivative chromosome was further confirmed to be a translocation chromosome 2 carrying segments from chromosome X, which originated from a segregation event of the maternal grandmother's balanced translocation passed on as a balanced translocation to the proband's mother either. So far, a number of candidate genes including EN1 on 2q were analyzed for Joubert syndrome. Based on our proband's abnormal karyotype, we suggest that further mapping studies for the syndrome should also be directed towards the chromosome X segments present on the derivative chromosome 2 of our proband.