OBJECTIVE: To study the effects of calcium on the choline peak measurements with 1H MR spectroscopy. MATERIAL AND METHODS: The thigh muscles of two cadaveric specimens were prospectively evaluated on a 3 T MR unit before and after the injection of calcium carbonate (up to 0.4322 g). The choline peaks of 147 spectra from 10 different anatomic locations were quantitatively evaluated. The influence of the calcium concentration and its disposition with respect to the main magnetic field were considered. B0 phase maps were used to evaluate field inhomogeneities. RESULTS: The presence of calcium led to a 43 % underestimation of the choline peak and the choline concentration (p = 0.0002 and 0.0036). The mean choline concentrations before and after CaCO3 injection were 3.53 ± 1.72 mmol/l and 1.58 ± 0.63 mmol/l. The influence of calcium carbonate on the choline peak estimations was proportional to the calcium concentration. There was a significant position-dependent difference in the estimation of the choline peak amplitude (p < 0.0154). Calcium injection led to a measurable increase in field inhomogeneities. CONCLUSION: There was a significant underestimation of the choline peak amplitude and concentration in the presence of calcium, which might cause misinterpretations of MR spectra. KEY POINTS: The presence of calcium led to significant underestimation of choline measurements. The influence of calcium is dependent on its concentration and distribution. Quantitative MR spectroscopy of calcified tumours should be interpreted with caution.