Confronted with the speed of technological advancements and increasing global competition, organizations have come to realize that their employees' continuous learning drives business success. A popular tool to support and enhance continuous learning is the personal development plan (PDP). Despite its popularity, empirical evidence of the effectiveness of the PDP is scarce. To date, most of the research on the practice of the PDP is conducted within educational (students) and health (general practitioners) settings and not within business environments. Moreover, research methodology is restricted to qualitative methods and survey research is rare. For that reason, we developed and validated a questionnaire to assess PDP practice. To develop the questionnaire, we relied on literature on portfolio assessment in the educational context and the workplace (health and education); to validate it, we collected data in three independent organizations. To assess the factor structure of the questionnaire, exploratory principal component factor analyses with direct oblimin rotation were conducted on data sets from two organizations. Factor reliability was computed using Cronbach's alpha coefficient. The principal component analysis resulted in a 35-item questionnaire containing five factors each with high internal validity. Cronbach's alphas ranged between 0.63 and 0.91. Next, a confirmatory factor analysis was conducted on an independent sample of 287 employees, working in a third organization. The results from this analysis were used to further refine the instrument. The present instrument provides a reliable and valid measure of the employee's perception of the PDP practice in the workplace, consisting of four scales and 19 items.