This study explored demographics and three characteristics of registered dietitians-optimism, perfectionism, and weight bias and whether they affect three components of dietetics practice-dietetics assessment, dietetics recommendations, and dietitian's perception of the client's success. Methods: A self-administered questionnaire was completed by 92 registered dietitians and student dietitians in New Zealand to assess explicit weight bias.[Correction added on 27 January 2023, after first online publication: in the preceding sentence, '109 registered dietitians' has been updated to '92 registered dietitians'.] Participants were randomised to receive a case study for a condition unrelated to weight accompanied by a photo of a woman with either a smaller or a larger body. Participants then assessed the client based on data provided, provided recommendations, and rated their perception of the client.Results: Mean (±SD) scores indicated mild fatphobia (2.63±0.39) in participating dietitians. Dietitians presented with the photo of a larger client assessed the client to have lower health and were more likely to provide unsolicited weight management recommendations. Additionally, dietitians rated the larger client as less receptive and motivated, and less likely to understand the recommendations adequately, with a lower ability to comply with and maintain these recommendations. Conclusions: Dietitians and student dietitians in New Zealand may practise in a manner that could be perceived as influenced by negative implicit weight bias, despite the explicit fatphobia scale scores assessing only mild fatphobia.Further research examining the extent of the problem in New Zealand, how it impacts client outcomes, and possible solutions are required.