The aim of this retrospective study was to investigate the accuracy of informant reports on cognitive status in mild cognitive impairment (MCI) by comparing the subjective evaluation made by patients’ relatives with the objective results of neuropsychological assessment. We enrolled 119 MCI outpatients and their relatives. Cognitive impairment was assessed by a battery of standardized neuropsychological tests. Informant reports on cognitive functioning were obtained by means of a structured interview. Subjective and objective evaluations of cognitive status were rated according to the same scoring system in order to enable comparison. All but one relative reported cognitive dysfunctions at the interview, but the kind of cognitive profile emerging from their reports was quite different from the one highlighted by neuropsychological assessment. A subjective evaluation of cognitive status based on informant reports could therefore be useful to identify patients with MCI but is unable to define MCI subtypes.