The n-back is a putative working memory task frequently used in neuroimaging research; however, literature addressing n-back use in clinical neuropsychological evaluation is sparse. We examined convergent validity of the n-back with an established measure of working memory, digit span backward. The relationship between n-back performance and scores on measures of processing speed was also examined, as was the ability of the n-back to detect potential between-groups differences in control and Parkinson's disease (PD) groups. Results revealed no correlation between n-back performance and digit span backward. N-back accuracy significantly correlated with a measure of processing speed (Trail Making Test Part A) at the 2-back load. Relative to controls, PD patients performed less accurately on the n-back and showed a trend toward slower reaction times, but did not differ on any of the neuropsychological measures. Results suggest the n-back is not a pure measure of working memory, but may be able to detect subtle differences in cognitive functioning between PD patients and controls.