An intervention study was conducted to investigate whether advanced ego development could be promoted if account was taken of the factors likely to be involved in the ego stage transition process in adulthood. A conceptual framework that identified such factors was described, in which it was hypothesised that stage transition occurs in response to life experiences that are structurally disequilibrating, personally salient, emotionally engaging, and interpersonal. The intervention was designed in accordance with these proposed types of life experiences, and was targeted toward adults at the modal stage of ego development. Using an experimental design, a significant increase in ego level was found in 2 equivalent intervention groups, with no increase found in a matched control group. The findings demonstrate the possibility of continued ego development in adulthood, including development to the advanced ego stages, and provide clarification regarding some of the processes involved in such development.