This article examines how firm growth is influenced by the strength of the industrial cluster in which the firm is located. It presents econometric estimates of firm growth for 56 two-digit industries in the UK. In about half of these industries, there is a positive and statistically significant association between firm growth and own-sector employment. Significant associations between firm growth and other-sector employment are less common, but where these arise they are generally negative. We find that a weak rule of thumb applies in most industries: own-sector effects are positive or insignificant, while other-sector effects are negative or insignificant. Cluster effects are strongest in manufacturing, manufacturing-related, and infrastructure, but weaker in services.