Hydrophobia may refer to one of the following:
- a set of symptoms of the later stages of a rabies infection, in which the victim has difficulty swallowing, shows panic when presented with liquids to drink, and cannot quench his or her thirst. "Hydrophobia" is also an old name for rabies itself.
- a phobia towards water, i.e., a morbid fear of water, or of swimming. It usually occurs in mild cases involving fear of deep water, and not as a general fear of the substance water. Aquaphobia is the more correct term, though "hydrophobia" has started to enter common use as a term for this phobia.
- a term used in chemistry to describe chemical "aversions" of a molecule or part of a molecule. For instance, a detergent is considered to have a hydrophobic tail and a hydrophilic head.