We present a boy diagnosed with partial 3p monosomy and partial 4q trisomy. The patient was 9 years of age with intellectual disability, dysmorphic features, and ataxia. A family history and medical evaluation showed that the father manifested similar facial dysmorphic features, intellectual disability, quadriparesis, and progressive cerebrospinal ataxia. The chromosomal aberration found in the proband was inherited from his father who was found to have a balanced reciprocal translocation of chromosomes 3p and 4q, which was in turn inherited from the paternal grandfather. The final cytogenetic diagnosis according to microarray was 46,XY,der(3)t(3;4)(p26.1;q32.2)arr 3p26.1(39,066–5,363,502)x1,4q32.2q35.2(162,555,236–191,173,881)x3. We describe the cytogenetic investigations that led to the identification of the breakpoints. In addition, we present an overview of the clinical features found in patients with partial 3p monosomies and partial 4q trisomies as reported in the literature. © 2012 Wiley Periodicals, Inc.