This paper uses the 1990–1998 Workplace Industrial Relations Survey Panel to analyse the impact of unions on employment growth among private sector workplaces in Britain. The growth rate among unionised workplaces was roughly 3–4% per annum lower than among non-unionised workplaces, ceteris paribus. The effect is not accounted for by the age of unionised workplaces, union concentration in declining industries, or organisational or technical change at workplace level. The effect remains once we account for the impact of unions on workplace survival. However, effects are only apparent where unions do not negotiate over employment and where unions have some degree of bargaining strength.