  We consider a 3-dimensional quantum antiferromagnet which can be driven
through a quantum critical point (QCP) by varying a tuning parameter g.
Starting from the magnetically ordered phase, the N{\'e}el temperature will
decrease to zero as the QCP is approached. From a generic quantum field theory,
together with numerical results from a specific microscopic Heisenberg spin
model, we demonstrate the existence of universal behaviour near the QCP. We
compare our results with available data for TlCuCl_3
