Microcephalic osteodysplastic primordial dwarfism is a rare disease characterized by unique clinical appearance and specific radiographic findings, and distinctive brain abnormalities. We describe the prenatal diagnosis of two siblings with microcephalic osteodysplastic primordial dwarfism types I/III at 23 and 26 weeks of gestation, respectively. Early detection by sequential antenatal sonographic evaluation is important for counselling families known to be at risk of this rare disease.