The objective of the study was to examine psychometric characteristics of two measures related to mental slowness experienced after stroke: One measure is aimed at performance on tasks, the other is a questionnaire evaluating perceived consequences of mental slowness. A group of 37 stroke patients and 33 matched controls were studied. A subgroup of 10 patients and 22 controls was observed by two independent raters to determine inter-rater reliability, a subgroup of 18 patients completed the questionnaire twice over a two-week interval to determine test-retest stability. Results showed that internal consistency was acceptable for the Mental Slowness Observation Test (Cronbach's alpha=.61 and .73) and good for the Mental Slowness Questionnaire (alpha=.91). For the Observation Test, correlations between the results of the two raters ranged between .77 and .99 and intra-class correlation coefficients were between .86 and .99. For the Questionnaire, correlations between two test occasions ranged between .85 and .90 and intra-class correlation coefficients were between .91 and .95. Correlations of between .52 and .67 were found between the Observation Test and neuropsychological tasks for speed of information processing. The Questionnaire correlated most strongly with scores on tests for activities of daily living (ADL) functioning, and fatigue and depression (correlations ranged between .37 and .63). It was concluded that the two new instruments offer reliable and valid methods for measuring limitations in daily activities related to mental slowness and some of the consequences of mental slowness in terms of sense of time pressure, fatigue, depressive complaints and independent ADL functioning.