In the majority of cases, acromegaly is sporadic. However, it can also occur in a familial setting as a component of MEN-1, MEN-4, Carney complex (CNC) or as the extremely rare syndrome of isolated familial somatotropinoma (IFS), the latter belonging to familial isolated pituitary adenomas (FIPA). The diagnosis of IFS is based on the recognition of acromegaly/gigantism in at least two family members, given that the family is not affected by MEN-1, MEN-4 or CNC. The authors present a case study of two sisters: a 56 year-old patient (case no. 1) and a 61 year-old patient (case no. 2). In both sisters, acromegaly was recognised in the course of pituitary macroadenoma. Neither of the sisters showed features of MEN-1, MEN-4 or Carney complex. The authors suppose that the presented cases are manifestations of IFS. However, this diagnosis has not been confirmed yet because of the poor availability of genetic tests.