It is imperative to understand the factors that influence clinical competency. Consequently, it is essential to study those that have an impact on the process of attaining clinical competency. A grounded theory approach was adopted for this study. Professional competency empowers nurses and enables them to fulfill their duties effectively. Internal and external factors were identified as affecting clinical competency. A total of 36 clinical nurses, nurse educators, hospital managers and members of the Nursing Council in Tehran participated in this (...) research. Data were obtained by semistructured interviews. Personal factors and useful work experience were considered to be significant, based on knowledge and skills, ethical conduct, professional commitment, self-respect and respect for others, as well as from effective relationships, interest, responsibility and accountability. Effective management, education systems and technology were named as influential environmental factors. Personal and environmental factors affect clinical competency. Ethical persons are responsible and committed to their work, acquiring relevant work experience. A suitable work environment that is structured and ordered also encourages an ethical approach by nurses. (shrink)