In an epidemiological study we assessed the evolution in the incidence and possible risk factors of knee injuries, especially anterior cruciate ligament (ACL) injuries, in Belgian soccer over one decade. Two soccer seasons (1999-2000 and 2009-2010) were compared and 56,364 injury reports registered by the KBVB-URBSFA were retrieved. Knee injuries totaled 9.971 cases, 5.495 in the first season (1999-2000) and 4.476 in the second (2009-2010): a significant decrease in incidence from 1.5 per 100 players in 2000 to 1.2 knee injuries in 2010. Six percent of all knee injuries were ACL injuries. The reported incidence of ACL tears slightly increased from 0.081 to 0.084 per 100 players. Female gender, competition and age over 18 years were prognosticators for ACL injuries. Enhanced prevention programs for ACL injuries, especially in those sports groups are warranted.