Diagnosaurus
- Sacroiliitis
- Saint Anthony's fire
- Salicylate poisoning
- Salivary gland inflammation
- Salivary gland tumor
- Salmonella gastroenteritis
- Salpingitis
- Sarcoidosis
- Scabies
- Schistosomiasis
- Schizophrenia
- Sciatica
- Scleritis or episcleritis
- Scleroderma
- Sclerosing cholangitis
- Seborrheic dermatitis
- Seborrheic keratosis
- Seizure
- Sepsis
- Septal perforation
- Septic arthritis (nongonococcal)
- Seronegative spondyloarthropathy
- Serous otitis media
- Sexual dysfunction, men
- Sexual dysfunction, women
- Sexually transmitted disease
- Shigellosis
- Shingles
- Shock
- Shunt (right to left, anatomic shunts)
- SIADH
- Sialadenitis
- Sialolithiasis
- Sicca syndrome
- Sickle cell anemia
- Sick sinus syndrome
- Silicosis
- Sinopulmonary syndromes
- Sinusitis, acute
- Sinusitis, chronic
- Sinus tachycardia
- Situational disorder
- Sjogren's syndrome
- Skin metastases
- SLE
- SLE, drug-induced
- Sleep, abnormal behaviors
- Sleep apnea
- Sleepiness, excessive
- Sleeping difficulty
- Sleeping sickness
- Small intestinal tumor
- Smallpox
- Smell, abnormal sense of
- Sodium, decreased serum
- Sodium, increased serum
- Somatoform disorder
- Sore throat
- Spinal cord compression
- Spinal cord metastases
- Spinal cord tumor
- Spinal stenosis, lumbar
- Spleen dysfunction and infection risk
- Spondylitis, ankylosing
- Spondyloarthropathy, seronegative
- Spontaneous abortion
- Spontaneous bacterial peritonitis
- Sporotrichosis
- Sprue, celiac
- Squamous cell carcinoma
- STD
- Stiffness
- Still's disease, adult
- Stomach tumor
- Stomatitis, ulcerative
- Streptococcal pharyngitis
- Stress disorder
- Stroke
- Strongyloidiasis
- Sty
- Subarachnoid hemorrhage
- Sudden death
- Superficial thrombophlebitis
- Superior vena cava syndrome
- Supraventricular tachycardia, paroxysmal
- SVT
- Sweating, excessive
- Sympatholytic poisoning
- Sympathomimetic poisoning
- Syncope
- Syphilis
- Systemic lupus erythematosus
- Systemic lupus erythematosus, drug-induced
- Systemic sclerosis