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Seventy-one healthy subjects with sleep disturbances participated in a randomized, double-blind controlled trial in which dietary supplementation with an extract of <i>Aloysia citrodora</i> (lemon verbena) (<i>n</i> = 33) or placebo (<i>n</i> = 38) was administered for 90 days. There were between-group differences in favor of the experimental group in the visual analogue scale (VAS) for sleep quality (6.5 ± 1.6 vs. 5.5 ± 2.1, <i>p</i> = 0.021) as well as in the overall score (5.8 ± 2.4, <i>p</i> = 0.008) and scores for sleep latency (1.6 ± 1.0 vs. 1.9 ± 0.7, <i>p</i> = 0.027) and sleep efficiency (84.5 ± 12.8 vs. 79.8 ± 13.6, <i>p</i> = 0.023) in the Pittsburgh Sleep Quality Index (PSQI). Sleep-related variables (latency, efficiency, wakefulness after sleep onset, awakenings) assessed by actigraphy also showed better scores in the experimental group (<i>p</i> = 0.001). Plasma nocturnal melatonin levels also increased significantly in the experimental group (199.7 ± 135.3 vs. 174.7 ± 115.4 pg/mL, <i>p</i> = 0.048). Changes in anthropometric parameters and physical activity levels were not found. In summary, a dietary supplement of lemon verbena administered for 3 months was associated with a significant improvement in sleep quality as compared with placebo in a population of healthy subjects with sleep problems.