This 1-year follow-up study (N = 841) investigated the relationship between boundary crossing behavior from work to nonwork and work-related rumination (i.e., affective rumination, problem-solving pondering, and lack of psychological detachment from work during off-job time). This relationship is important to examine as work-related rumination is a risk factor for poor recovery and ill-health over time. The aims were twofold: first, to examine these relationships in terms of temporal ordering, and, second, to show how individual differences regarding stability and change of boundaries from work to nonwork are reflected in work-related rumination across time. The structural equation modeling analyses lent support to the hypothesized normal causation model compared with the reversed causation and reciprocal models. However, only the cross-lagged relationship between high boundary crossing behavior at T1 and lack of psychological detachment at T2 was significant. Through latent profile analysis, 6 subgroups of boundary crossing behavior across time were identified. Over 70% of the employees belonged to the stable (low, moderate, high) and about one-third to the changing (mostly increasing) boundary crossing subgroups. Employees in the 2 stable (high and moderate) boundary crossing subgroups reported less psychological detachment and more problem-solving pondering during off-job time than did those in the low boundary crossing subgroup. Employees in the change groups reported simultaneous expected changes, especially in their problem-solving pondering. No effects on affective rumination were found. Thus frequent boundary crossing behavior from work to nonwork plays a different role regarding the various forms of work-related rumination during nonwork.