Abstract Introduction/Objective Structurally complex karyotypes are rarely identified in the postnatal constitutional setting. Abnormalities involving multiple chromosomes are likely to have a deleterious effect or be incompatible with life. Herein, we describe a case of a structurally complex karyotype in a newborn male. Methods/Case Report A newborn male presented at birth with microcephaly, severe ventriculomegaly, cerebellar hypoplasia and absent cavum septum pellucidum. Seizures, optic nerve dysplasia, and feeding difficulties were later noted. Microarray testing revealed eight small deletions of unclear significance on chromosome 7, with three located on the p arm and five clustered on the q arm. The deletions were gene poor, and none contained known haploinsufficient genes. Based on this finding a structural abnormality involving chromosome 7 was suspected. Karyotype revealed a structurally abnormal chromosome 7 and a complex rearrangement between chromosomes 11 and 18. Chromosome paint and metaphase FISH studies were performed to further characterize the abnormalities. Based on results from these cytogenetic tests, the observed abnormalities were characterized as an insertion on chromosome 7, and a translocation between chromosome 11 and 18 with an inversion on the derivative 18 [46,XY,ins(7)(p21q22q11.2),der(11)t(11;18)(q14.2;p11.2),der(18)(11qter→11q21::18q11.2→18p11.2::11q14.2→11q21:: 18q11.2→18qter)]. Rapid whole genome sequencing was done at an outside institution which was negative. Results (if a Case Study enter NA) NA Conclusion The exact cause of this individual’s phenotypic findings is unknown. Although the genomic imbalance detected by CMA is small, the complex structural abnormalities likely contribute to the clinical findings. Further supporting a deleterious effect of the karyotype findings is the negative whole genome sequencing results in this individual. Some apparently balance rearrangements have been shown to disrupt genes or important regulator elements. It is possible that a gene was disrupted at the breakpoint of one or more of the detected abnormalities or the rearrangement resulted in abnormal gene regulation. Additional submicroscopic abnormalities may also be present that were not detectable by the methodologies used.