High precision isotopic measurements of Sn in two commercially available high purity materials and a previously analysed cassiterite from Straits Settlement, Malaysia, are presented as a basis for a new measurement procedure using the Micromass IsoProbe MC-ICP-MS. The results show that under optimised instrumental conditions two laboratory calibration standard solutions (Johnson–Matthey Puratronic Grade 1 Sn metal foil and Specpure ICP/DCP Sn solution) are isotopically identical and an external reproducibility of 0.000017 2 s.d. at 150 ppb Sn concentration (122Sn/116Sn 0.318597, n = 14) can be achieved. An isotopic fractionation of +0.13‰/u (1.3 epsilon units) relative to these in-house standards has been verified for the cassiterite, which indicates a natural isotopic fractionation of approximately 2.8 times greater than the long-term reproducibility of the current optimised measurement procedure.