Cultivated sunflowers, Helianthus annuus L., show significant variation in susceptibility to insect pests, though specific mechanisms of resistance are not clear. Plant secondary compounds, including phenolics, are often associated with resistance to insects and pathogens. Because several phenolics are present in sunflower florets, wild sunflowers and cultivated inbred lines were sampled to document natural variation in free phenolics and evaluate their potential effects on floret-feeding pests. Four di-O-caffeoylquinic acid isomers were the largest contributors to total phenolic content of disc florets. When identified phenolics were combined with unidentified flavonoid glycosides, total phenolic concentration in inbred lines varied fourfold (≈ 18–72 mg/g), and was significantly greater than that in wild sunflowers. Two lab assays with 50 or 100 mg/g chlorogenic acid showed inconsistent reductions in mass or increases in mortality of sunflower moth (Homoeosoma electellum Hulst) larvae after 9 days, and tests using floret tissue with low or high levels of total phenolics did not show an effect of tissue type on H. electellum development. Tests for correlation between total phenolics and field data on susceptibility of sunflowers to another floret-feeding pest, banded sunflower moth (Cochylis hospes Walsingham), did not show any significant association. Cumulatively, results suggest there may be minor effects of phenolic compounds on floret-feeding insects, but these alone are insufficient for plant defense. However, variation in concentration of phenolic compounds may remain valuable, both as a component of plant defense and a source of oxidative stability in sunflower oil.