In this study, the effect of irrigation intervals (drought stress) on growth, predawn xylem water potential (Psi(w)), the osmotic potential at full turgor (Psi pi(100)), the osmotic potential at the turgor loss point (Psi pi(TLP)), osmotic adjustment and osmotic solutes (soluble sugars and proline) of Pinus pinea L. seedlings were examined. An experiment was carried out under greenhouse conditions using four watering treatments (control, 7-, 14-and 21-day irrigation intervals) in the first growth season; from mid-July to early November. Results showed that irrigation interval had significant effect on growth characteristics, Psi(w), water relation parameters, and osmotic solutes. The increasing irrigation interval significantly decreased the seedling height, root collar diameter, root, stem and needle dry weight, number of lateral branches, root percentage, root: shoot ratio and diameter: height ratio. Psi(w) and total soluble sugars decreased while proline content increased with the increase of drought stress. The Psi pi(100) and Psi pi(TLP) significantly decreased in drought-stressed seedlings compared to control (no stress) seedlings. The results suggest that the impact of drought stress increased with the increase of irrigation interval. Therefore, in the drought-stressed P. pinea seedlings were indicated osmotic adjustment by increasing the proline content and decreasing Psi pi(100) and Psi pi(TLP) during drought stress. Growth decreased under drought stress conditions in P. pinea seedlings.