We analyzed the triacylglycerol and phospholipid contents of hazelnuts from early development to maturity. Both were analyzed by high-performance liquid chromatography coupled to a light scattering detector. Trioleylglycerol, linoleyl-dioleylglycerol, and palmitoyl-dioleylglycerol were the most predominant triacylglycerols throughout development. Triacylglycerols showed small variation during hazelnut development. Phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol were the most abundant phospholipids. Traces of phosphatidic acid were also detected. The statistical analysis showed that the positive correlation among the individual phospholipid contents was significant. Phospholipid contents showed a steep decrease during hazelnut development. Triacylgycerols and phosphatidylcholine were isolated by preparative thin-layer chromatography, and their fatty acid profile was determined by gas-liquid chromatography. Triacylglycerols showed a high percentage of monounsaturated fatty acid moieties, whereas phosphatidylcholine had the highest percentage of saturated and monounsaturated fatty acid moieties. The polyunsaturated fatty acid moiety showed low percentages in the triacylglycerol and phospholipid backbone.