BACKGROUND/OBJECTIVES: Mild cognitive impairment (MCI), often considered as an early stage of dementia, is heterogeneous, and not all subjects with MCI progress into clinically diagnosed dementia. Low body weight (and body mass index, BMI) as well as losing weight while in MCI stadium have been proposed as possible risk factors of MCI-to-dementia conversion. SUBJECTS/METHODS: A prospective, 2-year observation of 102 MCI subjects has been conducted. Data on MCI subtype, somatic and neuropsychiatric co-morbidity and demographic characteristics (including age, gender and education), were collected. In addition, baseline and yearly BMI were calculated. RESULTS: Data of 83 out of the originally included 102 subjects were available after 2 years; 27 of those (32.5%) progressed to dementia. In univariate analysis, multiple-deficit MCI subtype (as compared with pure amnestic), higher age, the presence of diabetes and apathy, and lower baseline BMI (and losing weight on 2-year follow-up) were associated with conversion to dementia. Variables retained in the multivariate backward stepwise logistic regression model for conversion after 24 months of observation included lower baseline BMI (odds ratio, OR (95% cofidence interval, CI): 0.6 (0.4-0.9)), weight loss on 2-year follow-up (OR (95% CI): 1.3 (1.1-1.5)), male gender (OR (95% CI): 0.1 (0.01-0.9)) and presence of apathy (OR (95% CI): 70.7 (5.6-699)). Apathetic subjects had lower BMI and higher weight loss after controlling for potential confounders (age, gender, years of education and baseline ADAS-cog (Alzheimer's Disease Assessment Scale-cognitive subscale) score). CONCLUSION: MCI subjects presenting with apathy, low initial BMI and losing weight on follow-up have a significantly greater risk of developing dementia. Nutritional and behavioural assessment should be considered as additional tools in evaluating the risk of dementia among MCI subjects.