• Ollier's disease (chondrodysplasia) 756.4
  • Omentitis (see also Peritonitis) 567.9
  • Omentocele (see also Hernia, omental) 553.8
  • Omentum, omental - see condition
  • Omphalitis (congenital) (newborn) 771.4
  • Omphalocele 756.79
  • Omphalomesenteric duct, persistent 751.0
  • Omphalorrhagia, newborn 772.3
  • Omsk hemorrhagic fever 065.1
  • Onanism 307.9
  • Onchocerciasis 125.3
  • Onchocercosis 125.3
  • Oncocytoma (M8290/0) - see Neoplasm, by site, benign
  • Ondine's curse 348.8
  • Oneirophrenia (see also Schizophrenia) 295.4
  • Onychauxis 703.8
  • Onychia (with lymphangitis) 681.9
  • Onychitis (with lymphangitis) 681.9
  • Onycho-osteodysplasia 756.89
  • Onychocryptosis 703.0
  • Onychodystrophy 703.8
  • Onychogryphosis 703.8