Life history patterns of the three most abundant chironomids were analysed in Lake Balaton by monitoring the population dynamics of larvae and the presence of pupal exuviae. Procladius choreus had two generations per year with at least two parallel cohorts during 1996-1999. Tanypus punctipennis had a trivoltine life cycle with occasional parallel cohorts, overlapping generations and long, interrupted emergence periods between 1997 and 1999. At Tihany, Chironomus balatonicus had only one detectable generation between 1995 and 2002. Meanwhile at Keszthely, the abundance of C. balatonicus larvae peaked from autumn to the beginning of summer in 1996/1997, 1998/1999 and 2000/2001, and it was continuously high from August 2001 to October 2002. However, between these abundance peaks there were long periods when larvae could not be found at all. The extreme population dynamics of C. balatonicus suggests that living conditions may fluctuate around the limit of this species in Lake Balaton. Although C. balatonicus larvae practically were not found at both sampling sites from July 1997 to August 1998, and from July 1999 to August 2000, sporadic occurrence of exuviae during these periods proves that refuge areas should exist within the lake. Possible background of the uncommon population dynamics of C. balatonicus is discussed.