- Sympus 759.89
- Synarthrosis 719.80
- Syncephalus 759.4
- Synchondrosis 756.9
- Synchysis (senile) (vitreous humor) 379.21
- Syncope (near) (pre-) 780.2
- Syncytial infarct - see Placenta, abnormal
- Syndactylism, syndactyly (multiple sites) 755.10
- Syndrome - see also Disease
- Synechia (iris) (pupil) 364.70
- Synesthesia (see also Disturbance, sensation) 782.0
- Synodontia 520.2
- Synophthalmus 759.89
- Synorchidism 752.89
- Synorchism 752.89
- Synostosis (congenital) 756.59
- Synovial - see condition
- Synovioma (M9040/3) - see also Neoplasm, connective tissue, malignant
- Synoviosarcoma (M9040/3) - see Neoplasm, connective tissue, malignant
- Synovitis (see also Tenosynovitis) 727.00
- Syphilide 091.3
- Syphilis, syphilitic (acquired) 097.9
