This study aims to develop and validate a nursing assessment tool for patients with inflammatory bowel disease. In this cross-sectional descriptive study using a quantitative approach, nurses were invited to participate. The Delphi technique was used to obtain a consensus among expert nurses. Descriptive analysis was used for each item on the nursing assessment tool. Overall, 345 nurses were identified; 32 were eligible as experts and 13 validated the consultation. Of the 13 expert nurses, most were female (11, 84.62%), their mean age was 46.36 ± 10.59 years, eight (61.54%) graduated from public institutions, and eight (61.54%) had a master's degree. The initial version had 106 items, which was reduced to 95 items. The content of four domains (identification, health–disease profile, psychobiological needs, and physical examination) was validated in two rounds about the content with more than 80% of agreement. Two domains (sociodemographic data and health conditions, and personal cares) were validated in the first round with more than 80% of agreement. All domains were validated for their appearance during the first round with more than 80% of agreement. The Nursing Assessment Tool for Patients with Inflammatory Bowel Disease (IBD) had a considerable level of agreement regarding content and appearance validation in all dimensions.