BACKGROUND: Although nurses depend heavily on informal family caregivers to provide care to clients and to be involved in care planning and decision-making, no nursing theories that include the client, the caregiver, and the nurse were available to guide collaborative care planning and decision-making. AIM: The purpose of this paper is to describe the construction and initial testing of the theory of collaborative decision-making in nursing practice for a triad. The theory represents an extension of Kim's theory of collaborative decision-making in nursing practice. Kim's theory was developed to describe and explain collaborative decision-making in a dyad (client and nurse). The inclusion of a third person (family caregiver) in the theory required the addition of concepts about the caregiver, coalition formation, and nurse and caregiver outcomes. The expansion of Kim's dyadic theory to a triadic theory was achieved by means of a modified version of the theory derivation process described by Walker and Avant. CONCLUSIONS: The theory of collaborative decision-making in nursing practice for a triad can be used to guide further research and clinical practice. The theory provides a framework for researchers who are interested in studying the effects of collaboration regarding decision-making among nurses, family caregivers, and clients. The initial testing of the new theory in home health care nursing revealed variety in the nature of the client-caregiver-nurse relationships, the many processes used by the nurses in proceeding with the home visits, a multitude of decisions considered and different collaborative, noncollaborative, and coalition-forming interactions. The limited evidence of the empirical adequacy of the theory precludes development of definitive guidelines for clinical practice at this time. More studies are required before clinical practice guidelines can be developed. [ABSTRACT FROM AUTHOR]