The frequency of puerperal diseases was studied in a single, large, closed herd. Over a period of 24 months, treatment was given in connexion with 31% of 1360 farrowings. 25% of these treatments were based on the diagnosis mastitis and 75% on the less specific diagnosis farrowing fever. Statistical associations were investigated between these groups of diseases and factors such as time (season), disease and mortality in offspring, litter size, parity, and breed combinations. Major differences were found between the two syndromes, and, consequently, the common term MMA (Mastitis-Metritis-Agalactia) should not be applied. The major associations were found between farrowing fever and age and breed of the sow. Prospects of a frequency reduction are discussed.