Background: Pressure injuries (PI) are a significant clinical problem across all healthcare facilities, associated with poor patient outcomes, increased length of stay and healthcare costs. Whilst it is known that underweight (Body Mass Index (BMI) < 18.5 kg/m2) and malnourished individuals have an increased risk of developing PI, few studies have investigated the effects of obesity (BMI ≥ 30 kg/m2) and morbid obesity (BMI ≥ 40 kg/m2) on PI prevalence. This study aimed to determine whether PI prevalence was associated with levels of obesity; the complex association between morbid obesity, malnutrition and PI prevalence in hospital inpatients was also explored. Methods: Data collected from annual Queensland Patient Safety Bedside Audits conducted between 2010 and 2015 was used to examine the outcomes of interest (n = 2479). Bivariate tests were used to explore relationships between age, gender, BMI, malnutrition and PI prevalence. Regression analysis explored associations between BMI, malnutrition and PI, adjusting for potential confounders. Results: Overall PI prevalence was 6.9% and was significantly higher in the underweight and morbidly obese groups (underweight 12.7%, healthy weight 7.8%, overweight 5.7%, obese 4.8%, morbidly obese 12%; p = 0.001). In addition to BMI, malnutrition and age were significantly associated with PI prevalence. After adjusting for confounders, morbidly obese inpatients had over three times the odds of developing a PI compared to healthy weight inpatients (OR = 3.478, 95% CI 1.657–7.303; p = 0.001). Morbidly obese inpatients who were also malnourished had eleven-fold greater odds of developing a PI compared to the morbidly obese well-nourished in logistic regression analysis (OR = 11.143, 95% CI 2.279–54.481, p = 0.003). Conclusions: Morbid obesity is a significant and independent risk factor for PI development. However, the clustering of nutritional risk factors (morbid obesity and malnutrition) substantially increases this risk. Therefore, routine and formal assessment of both BMI and malnutrition status are important to enable the identification of patients at high risk of PI.