An adaptable ostomy base plate having a substantially convex shape for initial engagement with a peristomal skin surface and can be inverted to a substantially concave shape to fittingly engage to a topography of the peristomal skin surface for permanent engagement thereto. The base plate comprises a reinforcement ring arranged on a distal surface of the top film and the inner section of the base plate, being inside the reinforcement ring is provided with undulations defined by a series of concentric ridges and valleys, said series progresses outwardly from the stoma-receiving through-going hole towards the reinforcement ring and at least partly under the reinforcement ring.