Background Studies in mice have suggested that sarcopenic animals may have atrophic diaphragmatic muscles; however, to date, no clinical studies are available. Aims To investigate whether the diaphragmatic thickness is affected in older patients with sarcopenia and if this is associated with impaired respiratory functions. Methods Thirty sarcopenic and 30 non-sarcopenic elderly patients aged over 65 were included. All patients underwent comprehensive geriatric assessment. The diagnosis of sarcopenia was made according to the criteria of the European Working Group on Sarcopenia in Older People. Ultrasonographic evaluations of the patients were carried out by an experienced radiologist. Diaphragmatic thickness was measured in three positions: end of deep inspiration, quiet breathing, end of forced expiration. Peak expiratory flow (PEF) rate was evaluated by a peak flow meter. Results The mean age of the patients was 77 +/- 6 years, and 58% were females. Diaphragmatic thickness in three different positions (deep inspiration [2.3 mm (min-max: 1.3-4.1) vs. 2.5 mm (min-max: 1.9-4.9)], quiet breathing [1.8 mm (min-max: 1.0-2.8) vs. 2.00 mm (min-max: 1.3-3.9)] and end of forced expiration [1.1 mm (min-max: 0.7-2.5) vs. 1.5 mm (min-max: 0.5-3.4)]) were found to be thinner in sarcopenic patients compared to non-sarcopenics (p = 0.02, p = 0.02, p < 0.01, respectively). Also, PEF rate results were lower in patients with sarcopenia (245 L/min [min-max: 150-500] vs. 310 L/min [min-max: 220-610], p < 0.01). Diaphragmatic muscle thicknesses in all three positions were independently associated with sarcopenia status of the participants. Conclusions Our results suggest that sarcopenia in older people may be associated with reduced diaphragmatic muscle thickness and respiratory functions. Findings are needed to be confirmed in further multicenter studies with big sample sizes.