Objective Given the limitations of treatments for dementia, the characterisation of the early stages of dementia is crucial for the development of preventive programmes and interventions. We aimed to estimate the prevalence of mild cognitive impairment (MCI) and examine its medical and lifestyle correlates in a nationally representative sample of the Spanish population. Methods A total of 3625 participants (≥50 years of age) were interviewed in a cross‐sectional study. MCI was defined as the presence of cognitive concerns, the objective evidence of impairment in one or more cognitive domains, the preservation of independence in functional abilities and no dementia. Participants were also asked to provide sociodemographic, health status and lifestyle information. Logistic regression analyses were performed using the overall sample and by age groups. Results The overall prevalence of MCI was 9.6%, with higher rates in older people and women. In the overall model, after adjustment for potential confounders, depression [odds ratio (OR) = 1.79; 95% confidence interval (CI) = 1.21, 2.66], diabetes (OR = 1.43; 95% CI = 1.05, 1.95), sleep disturbances (OR = 1.66; 95% CI = 1.09, 2.55) and low level of physical activity (OR = 1.71; 95% CI = 1.26, 2.31) were associated with significantly higher odds for MCI. When stratified by age groups, depression (OR = 2.41; 95% CI = 1.35, 4.31), stroke (OR = 3.77; 95% CI = 1.44, 9.83) and obesity (OR = 2.06; 95% CI = 1.20, 3.53) were significantly associated with MCI in middle‐aged participants (50–64 years), whereas low level of physical activity (OR = 1.85; 95% CI = 1.32, 2.59) and sleep disturbances (OR = 1.79; 95% CI = 1.05, 3.05) were associated with MCI in individuals aged 65+ years. Conclusions Significant associations between MCI and psychological, cardiovascular and lifestyle factors were found. Targeting modifiable risk factors might reduce the risk for MCI and subsequent dementia.