Purpose: This manuscript describes the health information system security threat lifecycle (HISSTL) theory. The theory is grounded in case study data analyzing clinicians' health information system (HIS) privacy and security (P&S) experiences in the practice context. Methods: The 'questerview' technique was applied to this study of 26 clinicians situated in 3 large Australian (across Victoria) teaching hospitals. Questerviews rely on data collection that apply standardized questions and questionnaires during recorded interviews. Analysis (using Nvivo) involved the iterative scrutiny of interview transcripts to identify emergent themes. Results: Issues including poor training, ambiguous legal frameworks containing punitive threats, productivity challenges, usability errors and the limitations of the natural hospital environment emerged from empirical data about the clinicians' HIS P&S practices. The natural hospital environment is defined by the permanence of electronic HISs (e-HISs), shared workspaces, outdated HIT infrastructure, constant interruption, a P&S regulatory environment that is not conducive to optimal training outcomes and budgetary constraints. The evidence also indicated the obtrusiveness, timeliness, and reliability of P&:S implementations for clinical work affected participant attitudes to, and use of, e-HISs. Conclusion: The HISSTL emerged from the analysis of study evidence. The theory embodies elements such as the fiscal, regulatory and natural hospital environments which impede P&S implementations in practice settings. These elements conflict with improved patient care outcomes. Efforts by clinicians to avoid conflict and emphasize patient care above P&S tended to manifest as security breaches. These breaches entrench factors beyond clinician control and perpetuate those within clinician control. Security breaches of health information can progress through the HISSTI.. Some preliminary suggestions for addressing these issues are proposed. Study limita.tions: Legislative frameworks that are not related to direct patient care were excluded from this study. Other limitations included an exclusive focus on patient care tasks post-admission and pre-discharge from public hospital wards. Finally, the number of cases was limited by the number of participants who volunteered to participate in the study. It is reasonable to assume these participants were more interested in the P&S of patient care work than their counterparts, though the study was not intended to provide quantitative or statistical data. Nonetheless, additional case studies would strengthen the HISSTL theory if confirmatory, practice-based evidence were found.