Cytology: The medical and scientific study of cells. Cytology refers to a branch of pathology, the medical specialty that deals with making diagnoses of diseases and conditions through the examination of tissue samples from the body.

Cytologic examinations may be performed on body fluids (examples are blood, urine, and cerebrospinal fluid) or on material that is aspirated (drawn out via suction into a syringe) from the body. Cytology also can involve examinations of preparations that are scraped or washed (irrigated with a sterile solution) from specific areas of the body. For example, a common example of diagnostic cytology is the evaluation of cervical smears.

In order for cytologic evaluation to be carried out, the material to be examined is spread onto glass slides and stained. A pathologist then uses a microscope to examine the individual cells in the sample.