ABSTRACTData on large rockslides presented in a book by Olafur Jónsson (1976) are analyzed in terms of their magnitude and frequency in the Postglacial (10 000 a BP). Size has been examined by division into four groups, the modal size is from 1 to 10×106 m3. Age of rockslide events was assessed by relative methods by O. Johnsson and is thought to be internally consistent. Five age categories have been used and the modal group (III≈3–5000 a BP) has 34 % of rockslides. The period 3–7000 a BP contains 60% of all events; less than 5% have occurred in the last 1000 years. Age-size distributions suggest that the smallest slides are also the youngest; the largest events are the oldest. Problems associated with interpretation of the data are discussed in terms of a probability model but it is concluded that only a very simple interpretation is possible by its use. Climatic controls are not considered to be of prime importance in determining either size or age of slides. The majority of slides are found in lavas (Quaternary or Tertiary) and it is concluded that cleft water pressure (in some cases as a result of waning ice sheets) is the prime cause of slope failure.