BACKGROUND Rotavirus vaccination in infants has been reimbursed in Belgium since November 2006 and vaccine coverage is about 85%. OBJECTIVES: To assess and to compare the impact of mass rotavirus vaccination on the rotavirus related hospitalisations in children ≤5 y old pre-vaccination and up to 4 years post-introduction of the vaccine in 9 paediatric wards in Belgium.  METHODS: Stool samples for rotavirus detection were collected from all ≤5y old hospitalised children. The absolute number of rotavirus positive tests pre-vaccine launch (01/06/2004-31/05/2006) were compared with data at launch (01/06/2006-31/05/2007), and post-launch (01/06/2007-31/05/2011). Data are presented as a % reduction (95% CI) per year post-vaccination considering the annual average pre-vaccination period as a reference. RESULTS: The number of rotavirus-positive stool tests in children aged ≤5 years decreased from an average of 881 pre-vaccination to 600, a 32% reduction (95% CI: 29%-35%) during the launch period, to 368 (-58%, 95% CI: 55%-61%) in the 1st year post-launch, to 202 (-77%, 95% CI: 74%-80%) in the 2nd year, 180 (-80%, 95% CI: 77%-82%) in the 3rd year, and to 201 (-77%, 95% CI: 74%-80%) in the 4th year. In addition an overall decline (-38%, 95% CI: 36%-41%) in all-cause acute-gastroenteritis (AGE) related hospital admissions is observed from 1,757 per year pre-vaccination to 1,082 per year 4thyear post-launch. The number of bed days due to AGE has fallen from 8974 pre-vaccination to 5362 (-40%, 95% CI: 39%-41%) post-vaccination. A reduction from 6340 to 4894 (-27%, 95% CI: 26%-28%) is also seen amongst the non-rotavirus positive cases.  CONCLUSIONS: Significant declines in number of rotavirus and all-cause AGE related hospitalisations are seen in young children after 4 years of mass rotavirus vaccination in Belgium. A steady state may be reached after 3 years as no further decrease in the number of rotavirus related hospitalisations is observed.