China 
Africa 
- Shoulder injury
- Shoulder injury related to vaccine administration
- Shoulder joint
- Shoulder replacement
- Shoulder surgery
- Shrapnell's membrane
- Shuffling gait
- Shunt equation
- Shunt nephritis
- Shunting inhibition
- Shuttle vector
- Shwachman-Diamond syndrome
- Shy drager syndrome
- Shyness
- Sialadenitis
- Sialic acid
- Sialidase
- Sialidosis
- Sialin
- Sialoadenitis
- Sialoadhesin
- Sialocele
- Sialoglycoprotein
- Sialogogue
- Sialography
- Sialolithiasis
- Sialome
- Sialyltransferase
- Sibilant
- Sibiromycin
- Sibling abuse
- Sibling rivalry
- Sibutramine
- Sick building syndrome
- Sick sinus syndrome
- Sickle cell
- Sickle cell anemia
- Sickle cell crisis
- Sickle cell disease
- Sickle cell nephropathy
- Sickle cell retinopathy
- Sickle cell trait
- Sickness behavior
- Sida cordifolia
- Siddha medicine
- Side effects
- Side population
- Side reactions
- Side-chain theory
- Sideroblastic anemia
- Siderocalin
- Siderophores
- Siderosis
- Sidestream smoke
- Siesta
- Sievert
- Sight
- Sigma factor
- Sigma receptor
- Sigmoid
- Sigmoid colon
- Sigmoid sinus
- Sigmoidocele
- Sigmoidoscopy
- Sign language
- Sign test
- Signal detection theory
- Signal peptidase
- Signal peptide peptidase
- Signal peptides
- Signal recognition particle RNA
- Signal to noise ratio
- Signal transduction
- Signal transduction pathways
- Signal-regulatory protein
- Signaling protein
- Signaling theory
- Signalong
- Signalosome
- Signature-tagged mutagenesis
- Signatures
- Signet ring cell
- Signet ring cell carcinoma
- Silanes
- Silastic
- Sildenafil
- Silencers
- Silent hypoxia
- Silent mutations
- Silent sinus syndrome
- Silent synapses
- Silhouette sign
- Silica
- Silica gel
- Silicate
- Silicic acid
- Silicides
- Silicon compounds
- Silicon dioxide
- Silicon oxide
- Silicone elastomer
- Silicone gel
- Silicone gel sheeting
- Silicone granuloma
- Silicone hydrogel
- Silicone rubber
- Silicones
- Silicosis
- Silk
- Silkworms
- Silodosin
- Siltuximab
- Silver
- Silver Russell Syndrome
- Silver bromide
- Silver diamine fluoride
- Silver halides
- Silver iodide
- Silver nanoparticles
- Silver staining
- Silver sulfadiazine
- Silver-Russell syndrome
- Silvestrol
- Silybum
- Silybum marianum
- Silychristin
- Silymarin
- Simethicone
- Simian immunodeficiency virus
- Similac
- Similarity
- Simple View of Reading
- Simple cells
- Simple columnar epithelium
- Simple cuboidal epithelium
- Simple diffusion
- Simple face mask
- Simple hypothesis
- Simple partial seizure
- Simple sequence repeat
- Simple squamous epithelium
- Simplified molecular-input line-entry system
- Simpson's paradox
- Simpson-Golabi-Behmel syndrome
- Sims position
- Simtuzumab
- Simulated body fluid
- Simulated patient
- Simulator sickness
- Simulium