Are diaper usage overused in acute hospital settings? Are there ways to avoid unnecessary diaper usage? This study aimed to identify the prevalence of diaper usage and the reasons of using diaper as well as to suggest strategies to avoid unnecessary use of diaper. Diaper is widely used for patients in hospitals worldwide but is seldom to be report its prevalence. Some patients with medical issues need to use diaper but some who do not have those problems are still given a diaper to wear once admitted. This is a cross‐sectional prevalence survey study from 24 wards covering 3 major departments between 19 and 26 October 2016. Data were sourced from different means such as documents and interviewing patients/relative, nursing and nursing supporting staff. The study was approved by cluster general manager (nursing) who supported the study to improve patient care. The overall prevalence rate of diaper usage during admission was 37·9%. The top four reasons of diaper usage in all departments were faecal/urinary incontinence, poor patient condition, confusion and poor mobilization which accounted for 38, 15, 10 and 8% respectively. A total of 53 patients of those who had not used diapers before admission but were given diapers to wear, reported reasons as having poor mobilization and lower limb weakness. This is the first study ever to explore the prevalence and reasons of diaper usage in Hong Kong. Different reasons to use diapers after admission but patients did not use diaper upon admission could be identified in various department. A clinical guideline on proper use of diaper that identified some gaps of the prevailing practice and possible solutions was suggested to improve clinical practice.