Objective: To develop and validate a clinically feasible measure of communication effectiveness for people with any type of communication problem following stroke. Design: Cross-sectional, interview-based, psychometric study, building on the development phase for construction of the Communication Outcome after Stroke (COAST) scale. Setting: A community sample from the northwest of England, UK. Subjects: One hundred and two people with communication problems (aphasia and/or dysarthria) following a stroke, within the previous 4-12 months. Interventions: Administration of the COAST scale, on two occasions, within a two-week period, and collection of demographic and other data relating to disability, degree of aphasia (where appropriate) and hospital diagnosis of aphasia/dysarthria. Main measures: Acceptability (missing values), reliability (internal consistency and test-retest reliability) and item analysis (item redundancy). Results: Ninety-seven (visit 1) and 98 (visit 2) respondents provided usable data for the psychometric analysis. The 29-item COAST scale showed good acceptability (few missing values, sample spread 28-100%), internal consistency and test-retest reliability for the scale (α = 0.95; ICC = 0.90) and its subscales (α = 0.65-0.93; ICC = 0.72-0.88), but possible item redundancy. A revised scale of 20 items was produced, demonstrating good internal consistency and test-retest reliability (α = 0.83-92; ICC = 0.72-0.88). Conclusions: The COAST is a patient-centred, practical and reliable measure that can be used to assess self-perceived communication effectiveness for people with aphasia and/or dysarthria. Further testing on construct validity and responsiveness to change is needed before the measure can be firmly recommended for use within clinical practice and research. © 2008 SAGE Publications.