During the trial,174 patients with stable Crohn's disease will be divided into 2 groups. One group continues adalimumab injections with the same 2-week interval. And the other group will incrementally extend the interval to 4 weeks, under strict disease monitoring. If a step-down leads to recurrence of disease activity patients will return to the preceding effective dosing interval. Thus, we will investigate whether, and for whom, it is safe to extend the adalimumab injection interval.