Aims: Prescribing is a core skill for junior doctors, yet 8–10% of their prescriptions contain errors. To ensure adequate training in prescribing, it is important to define the diseases for which junior doctors should be competent to prescribe. The aim of the present study was therefore to identify the essential diseases in prescribing for junior doctors. Methods: A two-round Delphi consensus study was conducted among medical specialists, general practitioners, junior doctors, pharmacists and pharmacotherapy teachers from all eight academic hospitals in the Netherlands. Using a five-point Likert scale, the participants indicated for each item on an initial questionnaire whether it should be considered an essential disease for junior doctors. The items for which ≥80% of all respondents agreed or strongly agreed were accepted as essential diseases. Results: Sixty-two participants completed the Delphi survey. In total, 63 of 220 items were considered to be essential diseases. Conclusion: This is the first Delphi consensus study identifying exact conditions that junior doctors must be able to prescribe for. The essential diseases can be used for training in prescribing and assessment of junior doctors' prescribing competence.