Pycnodysostosis is an uncommon genetic disorder characterized by osteosclerosis of skeleton, short stature and bone fragility. The disease results from mutations in cathepsin K gene (CTSK) which is highly expressed in osteoclasts and crucial for the degradation of organic matrix from mineralized bone. Cathepsin K, a sistine protease, degrades bone matrix proteins, type I and type II collagen, osteopontin and osteonectin at low pH. Patiens have a typical appearance secondary to prominence of the calvarium, smallness of facial features, prominent nose and micrognatia. It resembles osteopetrosis with obvious bone sklerosis radiologically, and increased bone fragility; however the preservation of the medullary canal of long bones, increased mandibular angle and more rarely seen anemia distinguish it from osteopetrosis. We present a case, who, admitted with short stature, delayed closure of anterior fontanelle with similar cases in her family. She was diagnosed as by a pycnodysostosis simple radiological investigation

Keywords: Pycnodysostosis, delayed closure of anterior fontanelle