Extensive research supports the use of informant ratings in diagnosing dementia. In comparison, far fewer studies have examined the use of informant ratings in identifying mild cognitive impairment (MCI), a state that occurs as healthy older adults make the gradual transition to dementia. A review of available studies that have examined discrepancies between MCI patient and informant reports has for the most part demonstrated that informant ratings reveal greater loss of everyday functional ability and cognitive competency. Additionally, current findings support a significantly greater association of informant ratings with objective measures of patient cognitive performance and characteristics of underlying dementing processes. Structured measures used to examine the diagnostic efficacy of informant ratings in identifying cases of MCI are reviewed. Two recently developed instruments seem especially promising, but further validation efforts will be required before they can be considered to meet standards for clinical use.