In the spring of 1998, an outbreak of the cedar processionary moth (CPM) [Traumatocampa ispartaensis (Doganlar and Avci 2001)], a notodontid moth, began on 400 ha in a 75-year-old stand of Lebanon cedar (Cedrus libani A. Rich.) trees in the western Mediterranean region of Turkey. This was the first monitored outbreak of CPM in the Isparta region. Tree crowns recovered to near normal condition by the middle of each growing season (beginning of July) during the outbreak. From 1999-2003, CPM larvae were present in the same stands and again caused defoliation. The objective of this research was to explore dendrochronology as a means of determining the long-term role of CPM in tree growth and to quantify the historic importance of CPM. In 2003, increment cores were collected from 28 host and 10 nonhost dominant or codominant trees, and annual radial-growth indices from 1947-2003 were calculated for one nonhost and four host sample plots. Cedar tree-ring chronologies were analyzed for evidence of CPM. Tree-ring chronologies from nonhost cedar (undefoliated sample trees) were used to estimate potential growth in the host cedar (defoliated sample trees) during current and past outbreaks. The trees selected as host and nonhost were the same subspecies and varieties. We identified regional outbreaks of CPM by synchronous and sustained growth periods of the trees. Growth functions were defined as the cumulative sum of radial increments. Tree-ring evidence suggests that a large-scale outbreak began in 1954 (lasting from 1954-1961) and small outbreaks began in 1947 (1947-1951), 1985 (1985-1988), and 1998 (1998-2003) in the study area. The average reductions in diameter growth for the periods around 1947, 1954, 1985, and 1998 were 40, 28, 17, and 10% of potential, respectively. We concluded that a narrow latewood band is a significant historic indicator of defoliation by CPM, and the outbreaks appear to be associated with dry winter and spring weather prior to the fall and winter in which feeding occurred.