China 
Africa 
- Aspirator
- Aspirin
- Aspirin-exacerbated respiratory disease
- Aspirin-induced asthma
- Asplenia
- Asporin
- Assay sensitivity
- Assertive community treatment
- Assimilation
- Assisted feeding
- Assisted living
- Assisted living facility
- Assisted reproduction
- Assisted suicide
- Assisted ventilation
- Assistive technology
- Association
- Association constant
- Association cortex
- Association fibers
- Association mapping
- Association rules
- Association theory
- Associative agnosia
- Associative learning
- Associative memory
- Assortative mating
- Astacin
- Astasia abasia
- Astasia-abasia
- Astasis
- Astaxanthin
- Astemizole
- Aster tataricus
- Astereognosis
- Asterixis
- Asteroid hyalosis
- Asthenia
- Asthenopia
- Asthenospermia
- Asthenozoospermia
- Asthma
- Asthma exacerbation
- Asthma-COPD overlap
- Astigmatism
- Astragalin
- Astragalus
- Astragalus membranaceus
- Astringency
- Astringents
- Astroblastoma
- Astrocytes
- Astrocytoma
- Astrocytosis
- Astrogliosis
- Astroviridae
- Astrovirus
- Asunaprevir
- Asymmetric carbon
- Asymmetric cell division
- Asymmetric dimethylarginine
- Asymmetric flow field flow fractionation
- Asymmetric hydrogenation
- Asymmetric synthesis
- Asymptomatic bacteriuria
- Asymptomatic carriers
- Asymptomatic infection
- Asymptomatic inflammatory prostatitis
- Asynergy
- Asystole
- At risk mental state
- At-hook
- Atac-seq
- Ataluren
- Atavism
- Ataxia
- Ataxia telangiectasia
- Ataxia telangiectasia and rad3 related
- Ataxic
- Ataxic cerebral palsy
- Ataxic gait
- Ataxin
- Ataxin 3
- Atazanavir
- Atelectasis
- Atelectotrauma
- Atezolizumab
- Atg1
- Athanogene
- Athens insomnia scale
- Atherectomy
- Atherogenesis
- Atheroma
- Atherosclerosis
- Atherosclerosis Risk in Communities
- Atherosclerotic plaque
- Athetoid
- Athetoid cerebral palsy
- Athetosis
- Athlete's foot
- Athletic pubalgia
- Athletic trainer
- Athletic training
- Atipamezole
- Atkins diet
- Atlanto axial joint
- Atlanto occipital joint
- Atlanto-axial joint
- Atlanto-occipital dislocation
- Atlanto-occipital joint
- Atlantoaxial joint
- Atlantooccipital joint
- Atlas
- Atlastin
- Atmospheric aerosol
- Atmospheric composition
- Atmospheric deposition
- Atmospheric nitrogen
- Atmospheric pressure photoionization
- Atmospheric-pressure chemical ionization
- Atom
- Atomic absorption
- Atomic absorption spectrometry
- Atomic absorption spectroscopy
- Atomic emission spectroscopy
- Atomic nuclei
- Atomic ratio
- Atomic structure
- Atomization
- Atomoxetine
- Atonia
- Atonic seizures
- Atony
- Atopic dermatitis
- Atopic eczema
- Atopobium
- Atopobium vaginae
- Atopy
- Atorvastatin
- Atosiban
- Atovaquone
- Atox1
- Atractylodes
- Atractylodes macrocephala
- Atractyloside
- Atranorin
- Atransferrinemia
- Atrasentan
- Atraumatic restorative treatment
- Atrazine