Summary Background Many physicians believe that the most effective way to treat chronic urticaria is to take a nonsedating second‐generation H1‐antihistamine in the morning and a sedating first‐generation H1‐antihistamine, usually hydroxyzine, at night to enhance sleep. But is this belief well founded? Objectives To test this belief by comparing the effectiveness and prevalence of unwanted sedative effects when treating patients with chronic spontaneous urticaria (CSU) with levocetirizine 15 mg daily plus hydroxyzine 50 mg at night (levocetirizine plus hydroxyzine) vs. levocetirizine 20 mg daily (levocetirizine monotherapy). Methods In this randomized, double‐blind, cross‐over study, 24 patients with difficult‐to‐treat CSU took levocetirizine plus hydroxyzine or levocetirizine monotherapy for periods of 5 days each. At the end of each treatment period, assessments were made of quality of life (Chronic Urticaria Quality of Life Questionnaire, CU‐Q2oL), severity of urticaria symptoms (Urticaria Activity Score, UAS), sleep disturbance during the night and daytime somnolence. Results Both treatments significantly decreased UAS, night‐time sleep disturbances and CU‐Q2oL scores (P < 0·001) without significant differences between the two. Compared with baseline, daytime somnolence was significantly reduced by levocetirizine monotherapy (P = 0·006) but not by levocetirizine plus hydroxyzine (P = 0·218). Direct comparison of the two treatment modalities in terms of daytime somnolence favoured levocetirizine monotherapy (P = 0·026). Conclusions The widespread belief that sleep is aided by the addition of a sedating first‐generation H1‐antihistamine, usually hydroxyzine, at night is not supported. These results are in line with the urticaria guidelines, which state that first‐line treatment for urticaria should be new‐generation, nonsedating H1‐antihistamines only. What's already known about this topic? The EAACI/GA2LEN/EDF/WAO guideline for management of urticaria recommends second‐generation ‘nonsedating’ H1‐antihistamines as first‐line treatment for chronic spontaneous urticaria (CSU). However, it is common practice to add a sedating H1‐antihistamine, such as hydroxyzine, at night in the belief that it will reduce itch and improve the quality of sleep. What does this study add? This study compared 5‐day treatment of CSU with the second‐generation H1‐antihistamine, levocetirizine (20 mg daily), with levocetirizine (15 mg daily) plus hydroxyzine (50 mg nightly). The treatments were equally effective in decreasing symptoms and night‐time sleep disturbances and increasing quality of life, but the addition of night‐time hydroxyzine significantly increased daytime somnolence. The belief that addition of a night‐time sedating H1‐antihistamine is of benefit in the treatment of CSU is unfounded.