Objective: We investigated different dimensions of subjective cognitive decline (SCD) to determine which was the best prognostic risk factor for incident mild cognitive impairment (MCI) among cognitively unimpaired (CU) participants. Methods: We included 1167 CU participants, aged 70-95 years from the Mayo Clinic Study of Aging based on 2 concurrent SCD scales (part of the Blessed memory test and the 39-item ECog, which included a validated 12-item derivative) and a single question assessing worry about cognitive decline. We evaluated multiple ways to dichotomize scores. In continuous models we compared average scores on 4 ECog domains and multi-domain (39 and 12-item) ECog scores. Cox proportional hazard models were used to assess the association between each measure and risk of MCI in models adjusted for objective memory performance, depression, anxiety, sex, APOEε4 carriership and medical comorbidities. Results: It was possible to select a substantial group of participants (14%) at increased risk of incident MCI based on combined baseline endorsement of any consistent SCD on the ECog (any item scored ≥3; HR 12-item ECog 2.17 [1.51-3.13]) and worry (HR 1.79 [1.24-2.58]) in an adjusted model combining these dimensions. In continuous models, all ECog domains and the multi-domain scores were associated with risk of MCI with a small advantage for multi-domain SCD (HR 12-item ECog 2.13 [1.36-3.35] per point increase in average score). Information provided by the informant performed comparable to self-perceived SCD. Conclusion: Prognostic value of SCD for incident MCI improves when both consistency of SCD and associated worry are evaluated.