Objectives. Based on the lack of research on interventions targeting intrusive and worrisome thinking for insomnia, the aim was to examine whether a constructive worry (CW) intervention adds to the effects of behaviour therapy (BT).

Design. A randomized, controlled design was used. The design included a 2-week baseline, a 4-week intervention phase (sleep restriction and stimulus control [BT] or sleep restriction and stimulus control plus constructive worry [BT + CW]), and a 2-week follow-up.

Methods. Twenty-two patients with primary insomnia participated. The primary outcome was the Anxiety and Preoccupation about Sleep Questionnaire (APSQ), and secondary endpoints were subjective sleep estimates, the Insomnia Severity Index (ISI), and the Work and Social Adjustment Scale (WSAS).

Results. Although both conditions produced significant improvements in subjective sleep estimates, no significant group differences over time were shown for total wake time (TWT) and total sleep time (TST). Both interventions resulted in reductions over time in insomnia severity, worry, and dysfunction. Compared to BT, BT + CW led to a larger decrease in insomnia severity at all three time points (controlled d= 1.10–1.68). In comparison with BT, BT + CW resulted in a larger reduction in worry at two of the time points (controlled d= 0.76–1.64). No significant differences between the two conditions were demonstrated for dysfunction. While more participants responded positively to treatment in the BT + CW (80–100%) than in the BT condition (18–27%), none of the participants remitted.

Conclusions. The findings suggest that, compared to BT alone, CW might result in additional improvements in insomnia severity and worry. Given the small sample size and short follow-up, future studies are warranted.