The use of non-traditional scores in neuropsychological assessment allows for pattern analysis of test performance, commonly referred to as Quantified Process Approach (QPA). In the present study, the QPA was taken to study error rates on the Trail Making Test (TMT) in 26 non-demented patients with classic motor neuron disease (cMND), who commonly present with impaired cognitive flexibility, and 26 matched healthy controls. Between-group comparisons revealed that cMND patients exhibited higher total error rates on the TMT Part B (TMT-B) relative to controls (p < 0.001), though no significant associations were noted between TMT errors and measures of attention and executive function obtained using the Stroop Neuropsychological Screening Test, the Wechsler Adult Intelligence Scale Digit Symbol and Digit Span subtests and the Wisconsin Card Sorting Test. Moreover, the percentage of cMND patients with normal TMT-B time-to-completion who committed at least one error (either sequential or perseverative errors) in TMT-B was significantly higher compared to controls (p = 0.005). These findings suggest that error analysis using the QPA may increase the clinical utility of TMT and should be considered in addition to time-to-completion scores, in the neuropsychological assessment of patients with cMND.