Cognitive impairment may be detected largely by examining the performance on a single neuropsychological measure. The purpose of the present study was to evaluate the validity and diagnostic accuracy of a coding task in comparison with other related tasks. One hundred thirty-one first-episode psychosis patients were administered five cognitive tasks related to a "speed of processing and executive functioning" dimension (Digit Symbol, Trail Making Test [TMT] parts A and B, Cancellation Test, and Digit Span-backward) and an additional measure of functional outcome. Digit Symbol provided good indices of accuracy and correlations with the global composite score of a comprehensive neuropsychological assessment represented large effect sizes. Correlations with a functional outcome were modest. Similar results were observed with the TMT. The processing speed, as measured by Digit Symbol, may be particularly good in capturing the generalized dysfunction which may be causing the widespread cognitive failures in schizophrenia spectrum disorders.