AIM This paper presents a concept analysis of suboptimal care of the acutely unwell ward patient. BACKGROUND Acutely unwell patients exhibit abnormal vital signs which are either not recognized or are treated inappropriately. This is frequently termed 'suboptimal care'. However, use of the term 'suboptimal care' is ambiguous and not clearly defined. Critical review of this concept is required to ensure nurses have a better understanding of why and how suboptimal care occurs. DATA SOURCES Electronic databases (CINAHL, Medline, Cochrane) were searched for literature related to suboptimal care of acutely unwell ward patients. Reference lists from relevant publications were reviewed. No date or language restrictions were imposed. Only articles relevant to suboptimal care of the acutely unwell adult ward patient were included. All literature reviewed was in English and was published between 1990 and 2009. METHOD The Walker and Avant approach was used. RESULTS The attributes of suboptimal care are delays in diagnosis, treatment or referral, poor assessment and inadequate or inappropriate patient management. These attributes are preceded by contextual antecedents which can be categorized into patient complexity, healthcare workforce, organization and education factors. Suboptimal care may have catastrophic consequences for patients such as death, Intensive Care Unit admission or cardiac arrests which are preventable or avoidable. CONCLUSION For future research, investigators need to develop more objective measures which capture delays in the treatment and inappropriate or inadequate management of acutely unwell patients. This should occur through critical focus on the antecedents to suboptimal care.