In 14 men and nine women referred because of severe primary hypertriglyceridemia, our specific aim in a 54-week single-blind treatment (Rx) period was to determine whether triglyceride (TG) lowering with a Type V diet and Lopid would lead to improvement in symptoms of depression, improvement in an index of life stressors, change in locus of control index, and improved cognition, as serially tested by Beck (BDI), Hassles (HAS) and HAS intensity indices, Locus of Control index, and the Folstein Mini-Mental status exam. On Rx, median TG fell 47%, total cholesterol (TC) fell 15%, and HDLC rose 19% (all p < or = 0.001). BDI fell at all nine Rx visits (p < or = 0.001), a major reduction in a test of depressive symptoms. The HAS score also fell at all nine visits (p < or = 0.05 - < or = 0.001). Comparing pre-Rx baseline BDI vs BDI at 30 and 54 weeks on Rx, there was a major shift towards absence or amelioration of depressive symptoms (chi 2= 5.9, p = 0.016). On Rx, the greater the percent reduction in TG, the greater the percent fall in BDI (r = 0.47, p < or = 0.05); the greater the percent reduction in TC, the greater the percent fall in HAS (r = 0.41, p < or = 0.05). Improvement in the BDI and HAS accompanied treatment of severe hypertriglyceridemia, possibly by virtue of improved cerebral perfusion and oxygenation. There may be a reversible causal relationship between high TG and symptoms of depression.