BACKGROUND: Mild cognitive impairment with Lewy bodies (MCI-LB) is associated with a range of cognitive, motor, neuropsychiatric, sleep, autonomic and visual symptoms. We investigated the cumulative frequency of symptoms in a longitudinal cohort of MCI-LB compared with MCI due to Alzheimer's disease (MCI-AD) and analysed the ability of a previously described 10-point symptom scale to differentiate MCI-LB and MCI-AD, in an independent cohort. METHODS: Participants with probable MCI-LB (n=70), MCI-AD (n=51) and controls (n=34) had a detailed clinical assessment and annual follow-up (mean duration 1.7 years). The presence of a range of symptoms was ascertained using a modified version of the Lewy Body Disease Association Comprehensive LBD Symptom Checklist at baseline assessment and then annually. RESULTS: MCI-LB participants experienced a greater mean number of symptoms (24.2, SD=7.6) compared with MCI-AD (11.3, SD=7.4) and controls (4.2, SD=3.1; p<.001 all comparisons). A range of cognitive, parkinsonian, neuropsychiatric, sleep and autonomic symptoms were significantly more common in MCI-LB than MCI-AD, though when present, the time of onset was similar between the two groups. A previously defined 10-point symptom scale demonstrated very good discrimination between MCI-LB and MCI-AD (Area under the Receiver Operating Characteristic 0.91, 95% confidence interval 0.84-0.98), replicating our previous finding in a new cohort. CONCLUSIONS: MCI-LB is associated with the frequent presence of a particular profile of symptoms compared to MCI-AD. Clinicians should look for evidence of these symptoms in MCI and be aware of the potential for treatment. The presence of these symptoms may help to discriminate MCI-LB from MCI-AD.