Apathy is one of the most common behavioral symptoms in mild cognitive impairment (MCI). The aim of the authors' study was to examine the influence of the apathy dimensions, i.e., emotional blunting, lack of initiative, and lack of interest, on the risk of developing of Alzheimer disease (AD) in patients with MCI. Longitudinal study. Fourteen French memory clinics. Apathy was assessed in 214 MCI patients. The main endpoint considered was the development of AD during the 3-year follow-up. The neuropsychiatric evaluation included the Goldberg anxiety scale and the Montgomery and Asberg Depression Rating Scale; apathy was assessed with the Apathy Inventory. After 3 years, 59 patients (27.2%) had developed AD. The risk of conversion to AD was significantly higher for patients with lack of interest. Using Cox analyses, controlling for age, gender and education, the difference between survival curves was significant for lack of interest. Lack of interest, a mild behavioral sign, could be an indicator of potential decline in MCI patients and underlines the importance of checking the cognitive status of these patients.