Given the lack of data on dietary quality in young individuals with Prader–Willi syndrome (PWS) in Poland, a multiple case study was conducted in which anthropometric measurements and 7-day dietary records were collected from 20 subjects with PWS. The study group consisted of 8 females and 12 males with a mean age of 14.8 years and a mean BMI of 21.6. Based on BMI analysis, five subjects were overweight, including two subjects who were obese. The study showed that 35% of the subjects had energy intakes above the recommended levels. Protein deficiency was found in one subject in the analyzed diets. However, fat intake was excessive in four subjects, and the majority exceeded the recommended intake of saturated fatty acids. Vitamin E and B12 deficiencies were found in 40% and 85% of the subjects, respectively. All subjects had inadequate intakes of vitamin D and iodine, while the majority had deficiencies in sodium and copper intakes. Calcium intake was deficient in 35% of the subjects. However, most subjects met recommendations for the intakes of other minerals, vitamins, and fiber. These findings confirm the suboptimal dietary patterns of Polish individuals with PWS, with deficits observed in the intake of certain vitamins and minerals