<b><i>Aims:</i></b> To describe personality traits and their changes in mild cognitive impairment (MCI) and control subjects. <b><i>Methods:</i></b> Sixty-three MCI and 90 control subjects were asked to describe their current personality traits by the Structured Interview for the Five-Factor Model (SIFFM). For each subject, a close relative retrospectively assessed these descriptions both as to the previous and current personality traits, using the Revised NEO Personality Inventory, Form R (NEO-PI-R). <b><i>Results:</i></b> Self-assessed MCI subjects reported significantly lower scores in the openness dimension than control subjects [F(1, 150) = 9.84, p = 0.002, &#x03B7;_p² = 0.06]. In current observer ratings, MCI subjects had higher scores on neuroticism [F(1, 137) = 7.55, p = 0.007, &#x03B7;_p² = 0.05] and lower ones on extraversion [F(1, 137) = 6.40, p = 0.013, &#x03B7;_p² = 0.04], openness [F(1, 137) = 9.93, p = 0.002, &#x03B7;_p² = 0.07], agreeableness [F(1, 137) = 10.18, p = 0.002, &#x03B7;_p² = 0.07] and conscientiousness [F(1, 137) = 25.96, p < 0.001, &#x03B7;_p² = 0.16]. Previous personality traits discriminated the groups as previous openness [odds ratio (OR) = 0.97, 95% confidence interval (CI) = 0.95-0.99, p = 0.014] and conscientiousness (OR = 0.96, 95% CI 0.94-0.98, p = 0.001) were negatively related to MCI group membership. In MCI subjects, conscientiousness [F(1, 137) = 19.20, p < 0.001, &#x03B7;_p² = 0.12] and extraversion [F(1, 137) = 22.27, p < 0.001, &#x03B7;_p² = 0.14] decreased between previous and current evaluations and neuroticism increased [F(1, 137) = 22.23, p < 0.001, &#x03B7;_p² = 0.14], whereas no significant change was found in control subjects. <b><i>Conclusions:</i></b> MCI subjects undergo significant personality changes. Thus, personality assessment may aid the early detection of dementia.