We report on a girl with developmental delay, macrocephaly, facial asymmetry, small downturned palpebral fissures, high and narrow palate, micrognathia, short neck, a heart defect, and unilateral renal agenesis. Cytogenetic analysis showed a proximal tandem duplication of the long arm of chromosome one (1q12-->q21.3). This abnormality was suggested by G- and C-banding but it was specifically characterized by fluorescent in situ hybridization (FISH). Clinical findings in our patient are compared with those of the literature in an attempt to delineate the phenotype in patients with proximal 1q duplication.