Background: Malnutrition and poor growth are major problems for many patients with cystic fibrosis (CF), and nutritional supplements can enhance the success of dietary strategies. The purpose of this study was to assess Scandishake (Scandipharm Ltd, U.K.), an energy dense (2.0 kcal/ml) oral supplement. Methods: The study design included a 4‐week monitoring period, followed by 8 weeks of supplementation with Scandishake. The subjects had anthropometry assessed at weeks 0, 4 and 12, and their dietary intake assessed at weeks 0 and 12. Results: Data from 26 patients (16 male, 10 female; age range 9–34 years) showed a significant mean weight increase of 1.9 kg (range 1.6–4 kg) and a mean increase of 0.5 cm (range 1.1–2.7 cm) in mid‐arm muscle circumference. There was also an increase in energy intakes, rising from a mean of 11.15 MJ (2665 kcals) to a mean of 13.42 MJ (3208 kcals) ( P < 0.01), and the mean of individual percentages of estimated average requirement (EAR) for energy increased from 120% (73–182%) to 143% (67–221%). Conclusion: The energy dense formulation of Scandishake makes it a useful adjunct in the treatment of malnutrition and the promotion of normal growth in patients with CF.