BACKGROUND Pseudoachondroplasia (PSACH) is an autosomal dominant osteochondrodysplasia due to mutations in the gene encoding cartilage oligomeric matrix protein. It is characterized by rhizomelic dwarfism, limb and vertebral deformity, joint laxity and early onset osteoarthrosis. We present the girl with the early expressed and severe PSACH born to clinically and radiographically unaffected parents. METHODS A 6.5-year-old girl presented with short-limbed dwarfism (body height 79.5 cm, < P5;-32%) and normal craniofacial appearance and intelligence. The girl was normal until 3 months of age when she expressed growth retardation with apparently shorter extremities in relation to the torso. With age, her rhizomelic dwarfism became increasingly visible, and since completed 15 months of age, when she started to walk, the disease was complicated with genu varum, lumbar lordosis and abnormal gait. Beside visibly short forearms, short, broad and ulnar deviation of the hands, brachydactyly and joint hyperlaxity, the radiographic picture showed markedly flared metaphyses, small and irregular epiphyses and poorly formed acetabulum. CONCLUSIONS PSACH is an achondroplasia-like rhizomelic dwarfism recognized by the absence of abnormality at birth, normal craniofacial appearance, characteristic epiphyseal and metaphyseal radiographic finding and joint hyperlaxity.