Based on two independent personal cases and a pair of sibs from the literature, we delineate a new category of bone dysplasia with cup-shaped large metaphyses, for which the name metaphyseal acroscyphodysplasia is suggested. The main clinical features are severe growth retardation, micromelia predominating in the lower limbs, knee flexion, and severe brachydactyly. The radiological aspect of the knees is very specific: the lower femoral and upper tibial epiphyses embed themselves in their metaphyses, which are severely cup-shaped. Premature central epiphyso-metaphyseal fusion and gross deformation, or even coalescence, of the femoral condyles may occur. The femoral diaphyses are very short and broad, and there is progressive coxa valga. Bowed and/or short stubby tibiae with cone-shaped metaphyses, and varus deformity of the tibio-astragalian joint are other features. Slight deformations of the long bones occur in the upper limb. Severe brachydactyly, brachymesophalangy, phalangeal and metacarpal cone-shaped epiphyses and irregular, bent and shortened diaphyses are the main signs of hand involvement. Psychomotor retardation is present in 3/4. Autosomal recessive inheritance is likely.