This study investigated the potential and limitations of a self-fit hearing aid. This can be used in the “developing” world or in countries with large distances between the hearing-impaired subjects and the professional. It contains an on-board tone generator for in situ user-controlled, automated audiometry, and other tests for hearing aid fitting. Twenty subjects with mild hearing losses were involved. In situ audiometry showed a test-retest reliability (SD <3.7 dB) that compared well with the precision of diagnostic audiometry using headphones. There was good correspondence (SD <5.2 dB) with traditional pure-tone audiometry. In situ loudness scaling yielded important information about suprathreshold perception, which will have an added value for the selection of compression and the selection of maximum power output to be allowed in hearing aids.