- Ronidazole
- Rooming-in
- Root canal
- Root canal treatment
- Root exudates
- Root nodules
- Root of the mesentery
- Root of the penis
- Root planing
- Root resection
- Root resorption
- Root sheath
- Rooting reflex
- Ropinirole
- Ropivacaine
- Rorschach test
- Rorγt
- Rosa canina
- Rosa × damascena
- Rosacea
- Rosai-Dorfman disease
- Rose oil
- Roselle
- Rosemary
- Roseobacter
- Roseolovirus
- Rosiglitazone
- Rosin
- Rosmarinus
- Rosmarinus officinalis
- Ross River virus
- Ross procedure
- Ross' syndrome
- Rossmann fold
- Rostellum
- Rostral migratory stream
- Rostral ventrolateral medulla
- Rostral ventromedial medulla
- Rosuvastatin
- Rotary evaporator
- Rotation flap
- Rotational angiography
- Rotational correlation time
- Rotationplasty
- Rotator cuff
- Rotaviral gastroenteritis
- Rotavirus
- Rotavirus gastroenteritis
- Rotavirus vaccine
- Rote learning
- Rotenone
- Rothia
- Rothia dentocariosa
- Rothia mucilaginosa
- Rothmund-Thomson syndrome
- Rotigotine
- Rotor syndrome
- Rotterdam Study
- Rough endoplasmic reticulum
- Rough-and-tumble play
- Roughage
- Roughness
- Rouleaux
- Round ligament
- Round ligament of the liver
- Round ligament of the uterus
- Round window
- Roundup
- Rous sarcoma virus
- Routes of administration
- Roux en y gastric bypass
- Roux-en-Y
- Roux-en-y
- Rovalpituzumab tesirine
- Rovsing's sign
- Roxadustat
- Roxithromycin
- Royal jelly
- RpoB
- Rpob
- Rs4680
- Rs6265
- Rubber band ligation
- Rubber cement
- Rubber dam
- Rubbing alcohol
- Rubella
- Rubella vaccine
- Rubella virus
- Rubeosis iridis
- Rubinstein-Taybi Syndrome
- Rubinstein-Taybi syndrome
- Rubisco
- Rubivirus
- Ruboxistaurin
- Rubratoxin
- Rubrospinal tract
- Rubus
- Rubus idaeus
- Rubus occidentalis
- Ruby laser
- Rucaparib
- Rudimentary horn pregnancy
- Rudiviridae
- Rufinamide
- Rugae
- Rule of Rescue
- Rule of Six
- Rumack-Matthew nomogram
- Rumen
- Rumex crispus
- Rumination
- Rumination syndrome
- Ruminococcaceae
- Ruminococcus
- Run-in period
- Running economy
- Running-related injuries
- Runx2
- Runx3
- Rupatadine
- Rupintrivir
- Ruptured spleen
- Russell bodies
- Rut
- Ruta
- Ruta chalepensis
- Ruta graveolens
- Rutile
- Rutin
- Rutinose
- RuvC
- Ruxolitinib
- RxNorm
- Ryanodine
- Ryanodine receptor
- Ryanodine receptor 1
- Ryanodine receptor 2
- Rye
- S 100 protein
- S cell
- S phase
- S-23
- S-Adenosyl-L-homocysteine
- S-Glutathionylation
- S-Nitroso-N-acetylpenicillamine
- S-Nitrosoglutathione
- S-Nitrosothiol
- S-Nitrosylation
- S-layer