A poster produced by CRUK and the Scottish government, and distributed in Scotland, showed a calendar with sunbed appointments written on two dates in December, and a hospital appointment for cancer surgery on another date in March.
The advert said: "Using a sunbed could change your plans dramatically. Once a month or more on a sunbed can increase the risk of skin cancer by more than half."
The complainant said the advert misled people by implying it was possible to develop skin cancer within three and a half months of starting to use sunbeds.
In its response to the complaint, CRUK said it had not intended to suggest that cancer would develop within the space of three and a half months, and the poster showed the imaginary diary of a regular sunbed user.
The charity said the World Health Organisation had recently reclassified sunbeds as a group 1 carcinogen, the same category as cigarettes.
The ASA said consumers would understand the calendar image to refer to monthly sunbed use, rather than to imply that just two sunbed sessions would result in cancer surgery within the space of three and a half months. It ruled that the charity could continue to use the advert.