Objective To assess the effects of the copper intrauterine device (IUD) TCu-380A, on copper and zinc serum levels. Material and methods This longitudinal study enrolled 121 women attending Health Centres in Tehran between November 2011 and August 2012. A blood sample was obtained before use and three months after insertion of a TCu-380A IUD. Serum levels of copper and zinc were measured for the 101 women who had completed three months with the device in situ. Analyses of change included paired t-tests, McNemar tests and linear regression. Results Significant elevations in mean serum levels were found for both copper (170.22 μg/dl at three months vs.160.40 μg/dl at baseline, p = 0.034) and zinc (107.67 μg/dl at three months vs. 94.61 μg/dl at baseline, p < 0.001) three months after IUD insertion. Conclusions A slight, but significant increase in copper serum levels, not reaching toxic levels, was observed three months after TCu-380A IUD insertion. Zinc levels too had risen significantly, which was quite unexpected, and warrants further investigation.