There is a need to systematically assess vocational competency of adults with intellectual and developmental disabilities (IDD) according to the level of support they require. The present study reports on the development of the Client Profile Checklist (CPC) to assess vocational competency of adults with IDD. The 38 items that were selected from empirical literature and interviews with clinical staff were rated by training officers for 969 18 to 52-year-old trainees with IDD from low, medium, and high support level vocational training tracks. Factor analyses, multivariate analyses, ROC analyses, and reliability analyses were conducted to examine internal consistency, reliability, validity, and factor structure. Factor analyses yielded a conceptually acceptable 5-factor structure with 36 items accounting for 40.1% of the variance and with the internal consistencies of the subscales ranging from .52 to .81 (total items α = .85). The CPC total scores significantly differed across the three support levels. Cutoff scores for each track were also identified. In addition, inter-rater and test-retest reliabilities were high at .80 and .92, respectively. The preliminary results suggest that the CPC may be a useful tool for assessing vocational competency of adults with IDD according to the level of support they require.