This paper analyses the impact of a move from fractional to decimal pricing in the UK Long Gilt futures market, and thus offers a unique insight to tick size reduction and decimalization in a derivatives market setting. The reduced tick size leads to an increase in price clustering. The bid-ask spread, measured in ticks, increases following the tick size reduction. However, due to a reduced tick value, the monetary value of the spread declines. There is a substantial reduction in mean trade size as reduced-depth orders become trades. The mean daily number of transactions increases, which is entirely consistent with increased volume and decreased mean trade size. © 2005 Wiley Periodicals, Inc. Jrl Fut Mark 25:419–442, 2005