Monosomy 18p syndrome is a rare chromosomal disorder with varying phenotypic and clinical manifestations. Dysmorphism, growth delay, delayed speech and mental retardation are a few of the commonest features observed. The cytogenetic findings also vary and may comprise a pure deletion of the entire 18p arm or a deletion of a part of the 18p arm, if involved in a translocation with other chromosomes. Monosomy 18p may either occur by itself or with a structural alteration of the remaining chromosome 18, as a ring or as an isochromosome. The clinical presentation of this syndrome often overlaps with other syndromes. Establishing a cytogenetic diagnosis and understanding the location of the breakpoints is crucial for precise management and follow-up. We present here a rare case with mosaicism for a de novo deletion of 18p with isochromosome 18q in a boy born to a consanguineous Omani couple.