Real ear insertion gain was measured in 14 persons fitted with a variety of common assistive listening devices. Measurements were made in a quiet, but not soundproofed, clinical environment. The reliability of such insertion gain measures was studied, both for short-term and long-term test-retest conditions. The results indicated that insertion gain measurement of assistive listening devices can be performed as a routine clinical procedure. Intrasubject standard deviations were comparable in most cases to those clinically obtained using hearing aids with custom ear moulds.