Custodial grandparenting (i.e. raising grandchildren on a full-time basis) is a global phenomenon. Despite the hardships associated with 24/7 custodial care, grandparents continue to invest in their grandchildren. Why they do so is a matter of much conjecture. For example, it has been posited that grandparents assume custodial care of their grandchildren for reasons of necessity, altruism, aged-care reciprocity, or cultural continuity. This study examines the often overlooked issue of grandparent enjoyment as a motivating force behind custodial grandparenting caregiving investment. The results of our analysis of 88 completed Grandparent Needs, Wellbeing and Health Surveys determined that custodial grandparents' investiture in their grandchildren is influenced by three types of enjoyment, namely those derived from engagement in the child-centred nurturance of an at-risk grandchild, dyadic engagement in shared activities with their grandchild, and the personal grandparent-centred pleasure benefits to be had from fulfilling a grandcarer role. This study additionally reveals that informal custodial grandparents experience lower levels of closeness to their grandchild/ren, satisfaction with their grandparenting role, and assessment of their state of health than do formal (legal) custodial grandparents. The need to educate custodial grandparents of the potential health benefits to be had from investiture in their grandchildren is discussed.