- Iatrogenic syndrome of excess cortisol 255.0
- IBM (inclusion body myositis) 359.71
- Iceland disease (epidemic neuromyasthenia) 049.8
- Ichthyosis (congenita) 757.1
- Ichthyotoxism 988.0
- Icteroanemia, hemolytic (acquired) 283.9
- Icterus (see also Jaundice) 782.4
- Ictus solaris, solis 992.0
- Id reaction (due to bacteria) 692.89
- Ideation
- Identity disorder 313.82
- Idioglossia 307.9
- Idiopathic - see condition
- Idiosyncrasy (see also Allergy) 995.3
- Idiot, idiocy (congenital) 318.2
- IEED (involuntary emotional expression disorder) 310.8
- IFIS (intraoperative floppy iris syndrome) 364.81
- IgE asthma 493.0
- Ileitis (chronic) (see also Enteritis) 558.9
- Ileocolitis (see also Enteritis) 558.9
- Ileostomy status V44.2
- Ileotyphus 002.0