Background and aim: Variation in practice has been observed among the prescribed diets for inpatients with acute, uncomplicated diverticulitis. This study aimed to observe outcomes (length of stay (LOS), re-presentations, and gastrointestinal symptoms) for acute, uncomplicated diverticulitis inpatients prescribed restricted or liberalised diets during usual care. Methods: Adult inpatients with acute, uncomplicated diverticulitis were prospectively enrolled from 2017 to 2019. Demographics, clinical data, and prescribed diets were collected from medical records. Patients were categorised as having restricted or liberalised diets. Primary outcomes were LOS, re-presentations related to diverticulitis, and gastrointestinal symptoms, collected from medical records and patient surveys. Descriptive statistics were used to characterise all variables. Adjusted regression analysis was used to determine the effect of diet prescription on primary outcomes. Results: Of the 81 included patients, 47% were prescribed restricted diets, and 53% were prescribed liberalised diets. Patients prescribed restricted diets had greater LOS (median 4.0 (IQR: 3.5–5.1) vs. 2.8 (IQR: 2.2–3.8) days, p < 0.001) and were more likely to re-present due to diverticulitis at six months (OR 8.1, 95% CI 1.3–51.0, p = 0.025) in adjusted models. No difference in gastrointestinal symptoms was observed 30-days post-admission. Conclusion: In patients hospitalised with uncomplicated diverticulitis, restricted diets may be associated with longer LOS and increased odds of re-presentation at 6 months compared to liberalised diets. No differences in post-discharge gastrointestinal symptoms were observed between restricted versus liberalised diets. Randomised controlled trials are needed to confirm the causal role of inpatient diet prescription on clinical outcomes, healthcare utilisation, and patient experience. Registration: prospectively registered; ANZCTR Number: ACTRN12616001378415.