Having a decreased sense of security leads to unnecessary suffering and distress for patients. Establishing trust is critical for nurses to promote a patient's sense of security, consistent with trauma‐informed care. Research regarding nursing action, trust, and sense of security is wide‐ranging but fragmented. We used theory synthesis to organize the disparate existing knowledge into a testable middle‐range theory encompassing these concepts in hospitals. The resulting model illustrates how individuals are admitted to the hospital with some predisposition to trust or (...) mistrust the healthcare system and/or personnel. Patients encounter circumstances increasing their emotional and/or physical vulnerability to harm, leading to experiences of fear and anxiety. Without intervention, fear and anxiety lead to a decreased sense of security, increased distress, and suffering. Nurse action can ameliorate these effects by increasing a hospitalized person's sense of security or by promoting the development of interpersonal trust, also leading to an increased sense of security. Increased sense of security results in diminished anxiety and fear, and increased hopefulness, confidence, calm, sense of value, and sense of control. The consequences of a decreased sense of security are harmful to patients and nurses should know that they can intervene in ways that both increase interpersonal trust and sense of security. (shrink)