Background: The Test of Masticating and Swallowing Solids (TOMASS) is an international standardized swallowing assessment tool. However, its psychometric characteristics have not been analysed in patients with dysphagia. Aims: To analyse TOMASS's (1) inter- and intra-rater reliability in a clinical population of patients with dysphagia, (2) known-group validity, (3) concurrent validity and (4) correlation with meal duration. Methods & Procedures: Two age- and gender-matched groups of 39 participants each were recruited: A group of patients with dysphagia and a control group with no history of dysphagia. The TOMASS was carried out in both populations, video-recorded and scored offline by two speech and language therapists (SLT 1 and SLT 2) (inter-rater reliability) and twice by the same SLT (intra-rater reliability). In the clinical group, the TOMASS was carried out three times: (1) to verify understanding of the required tasks, (2) performed concurrently during fibreoptic endoscopic evaluation of swallowing (FEES) to assess validity and (3) during clinical assessment to assess reliability. TOMASS under endoscopic control was recorded and the number of white-out events was counted to compare with the number of observed swallows per cracker during standard TOMASS as a measure of concurrent validity. As additional measures of TOMASS validity, oral dental status, classified as 'functional' or 'partially functional', and duration of a standard meal were assessed by an SLT (SLT 1 or SLT 2), and then correlated with TOMASS. Outcome & Results: TOMASS's inter- and intra-rater reliability were high (intraclass correlation coefficient (ICC) > 0.95) in both the clinical and the control groups. The number of masticatory cycles (p = 0.020), swallows (p = 0.013) and total time (p = 0.003) of TOMASS were significantly lower in the control group than in the clinical group. Patients with 'partially functional' oral dental status showed a significantly higher number of masticatory cycles per cracker and a longer duration of ingestion than patients with a 'functional' one. Concurrent validity suggested a substantial agreement between TOMASS and FEES in defining the number of swallows per cracker. The mean difference of the two measures was -0.02 (95% confidence interval (CI) = -1.7 to 1.2). Meal duration significantly correlated with the 'number of swallows per cracker' (r = 0.49; p = 0.002) and 'total time' (r = 0.41; p = 0.011). Conclusions & Implications: Preliminary psychometric analysis of TOMASS in a clinical sample of outpatients with dysphagia suggests that it is a reliable and valid (specifically related to the number of swallows per cracker) tool. TOMASS's application in clinical practice to quantitatively measure solid bolus ingestion is recommended.