This study examined the relationship between the bowling workload of first-class cricket fast bowlers and injury with the aim of identifying a workload threshold at which point the risk of injury increases. Ninety male fast bowlers (mean age 27 years, range 18-38 years) from six Australian state squads were observed for the 2000-2001 and/or 2001-2002 cricket seasons. Workload was quantified by examining fixture scorecards and conducting surveillance at training sessions. Injury data was obtained from the Cricket Australia's Injury Surveillance System. Compared to bowlers with an average of 3-3.99 days between bowling sessions, bowlers with an average of less than 2 days (risk ratio (RR) = 2.4, 95% confidence interval (CI) 1.6 to 3.5) or 5 or more days between sessions (RR = 1.8, 95% CI 1.1 to 2.9) were at a significantly increased risk of injury. Compared to those bowlers with an average of 123-188 deliveries per week, bowlers with an average of fewer than 123 deliveries per week (RR = 1.4, 95% CI 1.0 to 2.0) or more than 188 deliveries per week (RR= 1.4, 95% CI 0.9 to 1.6) may also be at an increased risk of injury. There appears to be a dual fast bowling workload threshold beyond which the risk of injury increases and maintaining a workload that is too low or infrequent is an equally significant risk factor for injury as maintaining a high bowling workload. Further study is required to determine the reason why players who bowl infrequently suffer more injuries.