To explore how CNCs who provide hospital wide support after hours (AHCSs) construct their role. This is an ethnographic study involving two AHCSs as participants. Audio visual data was collected in 2007 at a Major Metropolitan Hospital, Sydney during after hours shifts. The data was coded using the standards defined in the Nurse Practitioner (NP) competencies. Four hours of videotape (observed clinical practice) and 2 h of audio tape (interviews) were coded. They performed procedures (22%), gathered information to identify at risk patients (21%), conducted patient assessments (20%) and relayed information/findings to ward nurses (12%) and doctors (12%). The roles/responsibilities of AHCSs were similar to those defined for NPs. For the domain “dynamic practice” 388 activities were identified. The two participants used advanced and comprehensive assessment skills and demonstrated a high level of proficiency in performing procedures/interventions. For the domain “professional efficacy” 174 activities were coded, for “clinical leadership” there were 135 activities. “Pro-actively identifying at risk patients in general wards” was added as a new performance indicator within the domain “clinical leadership”. An analysis of the interviews corroborated the results derived from the visual data. A significant capacity for critical thinking and clinical decision making were the hallmarks of the performance of the two AHCSs; their style of practice was collaborative, flexible and autonomous. While their formal role were as CNCs the two participants operationalised their roles/responsibilities as would a Nurse Practitioner. Their practice demonstrated a new competency: “the pro-active identification of at risk patients”.