- Sarcoma (bone cancer)
- SARS
- Scabies
- Scarlet fever
- Scars
- Schistosomiasis
- Schizophrenia
- Sciatica
- Scleroderma
- Scoliosis
- Scurvy
- Seasonal affective disorder
- Seasonal allergic rhinitis
- Selective serotonin reuptake inhibitors
- Self-injury
- Septic shock
- Sex change
- Sexual health clinics
- Sexually transmitted infections
- Shingles
- Short-sightedness
- Shoulder pain
- Sick building syndrome
- Sickle-cell anaemia
- Sickness and diarrhoea in children
- Singultus
- Sinusitis
- Sjogren's syndrome
- Skin cancer (malignant melanoma)
- Skin cancer (non-melanoma)
- Slapped cheek syndrome
- Sleep apnoea
- Slipped disc
- Small bowel transplant
- Smear test
- Smelly feet (bromodosis)
- Smoking (quitting)
- Snake bites
- Snoring
- Solvent abuse
- Sore throat
- Spina bifida
- Spinal muscular atrophy
- Sports injuries
- Sprains and strains
- Squint
- SSRIs (selective serotonin reuptake inhibitors)
- Staphylococcal infections
- Statins
- Stem cell transplant
- Stillbirth
- Stings, insect
- Stings, marine creatures
- Stoma
- Stomach cancer
- Stomach ulcer
- Streptococcal infections
- Stress
- Stress incontinence
- Stretch marks
- Stria
- Stroke
- Subarachnoid haemorrhage
- Subdural haematoma
- Sudden infant death syndrome (SIDS)
- Suicide
- Sunburn
- Supraventricular tachycardia
- Sweating, excessive (hyperhidrosis)
- Swimmer's ear
- Swine flu
- Syphilis
- Systemic lupus erythematosus