Simpson's appearances during the 1965–66 Ashes series were intermittent. He missed the First Test due to a broken wrist, which ended in a draw under the leadership of Booth. He returned for the Second Test at Melbourne, scoring a half-century in both innings of a drawn match. Chickenpox forced him to miss the Third Test, which Australia lost by an innings. It was the first time that Australia had lost by an innings since 1956, and the selectors responded by dropping four players including Booth. On his return for the Fourth Test at Adelaide Simpson made 225, making 244 runs in 255 minutes with Lawry, the highest opening stand by Australia against England and still the highest against England in Australia. Australia claimed a decisive innings victory to level the series and a draw in the Fifth Test allowed Australia to retain the Ashes. Simpson topped the batting averages with 355 runs at 88.75 average.