It was early 1990 that we had gathered at Arnie Levine’s home for dinner to celebrate the transition of several postdoctoral fellows to faculty positions in academia. As a new postdoctoral fellow in his lab, I was thrilled to have the opportunity to spend some personal time with Arnie. We were discussing the paradigm shift made by his group a year earlier that p53 is a tumour suppressor (Finlay et al., 1989) and not an oncogene, as originally thought for a decade after its original discovery (Lane and Crawford, 1979; Linzer and Levine, 1979). Paraphrasing Arnie’s comment about this landmark discovery, he said that it was fun, a really big wave to ride, and not to worry as there will be more to come. Unknowingly at the time, that prediction led to the identification of Mdm2 as a negative regulator of p53. This perspective revisits some personal experiences of training as a postdoctoral fellow under the mentorship of Dr Arnie Levine and highlights several key experiments that established Mdm2 as the negative regulator of p53.