C90 or C-90 may refer to:
Science and technology Multiple myeloma and malignant plasma cell neoplasms (ICD-10 code) Caldwell 90 (NGC 2867), a planetary nebula in the constellation Carina C, the conventional electrical unit for the coulomb C90 audio cassette, a blank audio cassette in the very popular 90 (2 x 45) minute length
Computing Cray C90, a supercomputer C90 (C version), a standardized ISO C form of the C programming language, virtually the same as the ANSI C ("C89") standard
Transportation Beechcraft C90 King Air, an aircraft Continental C90, an aircraft engine Honda Super Cub, an underbone motorcycle designated C90 in a 90 cc version Chicago terminal radar approach control, (FAA designation C90); See Air traffic control
Other uses C90-CR (M3), a rocket launcher Ruy Lopez chess openings (ECO code)