The aim of the present study was to determine the relationships between serum lithium level, duration of lithium intoxication, severity of symptoms, and the outcome of the disease. Subjects with a serum lithium level of >/=1.2 mEq/L were included in the study. Seventy-eight patients with lithium intoxication were identified between 1 July 1999 and 31 December 2002. The demographic characteristics, clinical manifestations, and concomitant medications were recorded. Most patients with acute lithium intoxication had mild symptoms, independent of the serum lithium levels. In patients with chronic lithium intoxication, the frequency of severe symptoms was higher than in those with acute intoxication. None of the 78 intoxicated patients in the present survey died or suffered from persistent neurological sequelae. Patients with concomitant medications, older age, and existing neurological illness may have an increased susceptibility to lithium toxicity. Regular monitoring of serum lithium level is essential for lithium-treated patients. Clinicians should pay attention to patients with pre-existing neurological illness, older age, or receiving medications that may interact with lithium.