Introduction The aim of this study was to test whether (i) sense of belonging with work predicted sleep quality or if (ii) sleep quality predicted sense of belonging with work. Both hypotheses are likely since the feeling of not belonging to a group is highly stressful, and since disturbed sleep may lead to hostility and poor relationships.

Methods The longitudinal WOLF project was used. Of the invited 5092 individuals, 4715 (93%) filled out a questionnaire in 1996–1998 (T1). The follow-up response rate was 71% (n = 3637) at T2 and 66% (n = 2420) at T3. The average follow-up time was 5 years between T1 and T2 and 7 years between T2 and T3. Sense of belonging was assessed by two questions on belongingness with the company and with coworkers. Sleep quality was assessed by the Karolinska Sleep Questionnaire. Logistic regression was used.

Results Sense of belonging with work did not predict sleep quality. Disturbed sleep quality at both T1 and T2 (OR 1.66, 95% CI: 1.24–2.28) and deteriorating sleep quality between T1 and T2 (OR 1.69, 95% CI: 1.21–2.36) increased the risk of poor sense of belonging with work at T3 compared to those reporting good sleep quality at T1 and T2. Good sleep at both T1 and T2 (OR 0.59; 95% CI: 0.42–0.83) and improved sleep quality (OR 0.50; 95% CI: 0.29–0.85) decreased the risk of poor sense of belonging with work at T3 compared to those with disturbed sleep at T1 and T2.

Conclusion Poor and deteriorating sleep quality increased the risk of not feeling included in the work group whereas good and improved sleep quality decreased this risk. Feelings of exclusion have been shown to predict serious disease. Intervening with sleep problems and consequently increasing feelings of inclusion, may thus be health promotive.