Grimble and Fairbairn's recently published results on H∞robust self-tuning control are discussed. It is pointed out that further explanation about the system model is needed, and the identified system model should be revised. Grimble (1987 a, b) and Fairbairn and Grimble (1990) give a new approach to designing self-tuning controllers for SISO discrete-time stochastic systems. There are some points that call for further discussion.