Before preparation of the compounded medicine a pharmacist must check the correctness of the prescription, with the most important control of dosages of active substances. The inspection should concern not only the maximum single dose, but also maximum daily dose. A dose of the active substance prescribed for an adult patient is compared with the maximum permissible dose listed in the Polish Pharmacopoeia (FP), always considering the route of administration. If a dose is larger than the maximum dose defined by FP, and the physician did not make a clear note on this fact in the prescription, the pharmacist before compounding the medicine must consult the physician to ensure that the dose is deliberately exceeded. Otherwise the dose must be reduced to the pharmacopoeial maximum dose. For pediatric patients the maximum dose is calculated based on the maximum dose for adults. Appropriate equations taking into account either child’s age (Young’s, Cowling’s and Fried’s equations), or body weight (Clark’s equation) or body surface are in use. In the article these rules are summarized and compared as well as relevant problems are indicated.