Objective: This study explored how psychologists in Australia assess and diagnose adults with dyslexia. Psychologists' understandings about dyslexia were recorded alongside the tools used for diagnosing adults with dyslexia (and how these differ from practices with young people). Training experiences and influential factors on diagnostic decision-making in assessing adults for dyslexia were identified. Method: An online survey, based on the study aims, was distributed to various professional associations. Participants were 32 registered psychologists in Australia who had assessed adults for dyslexia. Survey responses were analysed using descriptive statistics and non-parametric analyses. Results: Most participants reported: (1) that dyslexia is attributable to deficits in phonological processing and rapid automatized naming, (2) assessing adults for dyslexia involves the administration of Wechsler cognitive and achievement tests, (3) familiarity with test tools, diagnostic criteria, and clinical judgement informed adult-focused dyslexia assessment practices, (4) adults and children are assessed for dyslexia in similar ways, and (5) there is little post-registration training specific to assessing adults for dyslexia. Conclusions: Psychologists extrapolated child-focused dyslexia assessment practices to adults. This may result in a missed dyslexia diagnosis and/or expending unnecessary resources on assessment. There is a need for increased training in developmentally-sensitive methods for assessing adults for dyslexia.