Background: Pressure injuries on mucous membranes are caused by pressure from medical devices at the site of injury and differ to those on the skin. Intensive care patients, who have multiple devices in situ, are particularly vulnerable. There is a significant knowledge gap regarding mucous membrane pressure injury (MMPI) incidence in acute hospital settings. Aim:To analyse MMPI incidence and characteristics in a tertiary acute general hospital. Methods:A secondary data analysis of hospital clinical incident reports was conducted. The sample included all adults with MMPIs between 2015 and 2019. The STROBE reporting guideline was followed.Results: There were 414 reports of MMPI. Most (91.5%, n = 379) were hospital-acquired with the majority found in intensive care patients (74.4%, n = 282). Hospital-acquired MMPI incidence was 0.1% (11 MMPI per 10,000 hospital episodes). In intensive care, the incidence was 2.4% (235 MMPI per 10,000 intensive care episodes). The median time from device insertion until reporting of an MMPI was 3 days. The most common sites of mucosal injury were the lips (35.6%) and mouth (28.8%). In all cases except one, MMPI was associated with medical device use at the site of injury. Five device types were identified (oral endotracheal tube-related 70.3%; urinary catheter 15.5%; gastric tube 8.3%; nasal prongs 3.5%; tracheostomy tube 2.4%). In intensive care, oral endotracheal tube-related devices were most often associated with MMPI (84.8%), whereas in non-intensive care MMPI it was the urinary catheter (51.4%).Conclusions: While hospital-acquired MMPI incidence is relatively low, it is considerably higher in intensive care patients compared to those in non-intensive care settings. The most common sites are the lips and mouth.Relevance to clinical practice: Mucous membrane pressure injuries represent a significant proportion of all hospital-acquired pressure injuries.Patient or public contribution: Neither patients nor the public were directly involved in this project.