The number of cases of Mycoplasma pneumoniae infection detected by laboratory-based surveillance increased in Finland in late 2010. During 2011, the number of cases was four times higher than during the previous epidemic in 2005. The 2011 epidemic affected mostly school-age children. The number of cases dropped between April and July 2011 and then started to increase again in September 2011. The number of cases rose from 1,948 (36.2 per 100,000 population) in 2010 to 7,772 (145 per 100,000 population) in 2011.