Caspar David Friedrich (1774 - 1840) is one of the most important German Romantic painters. In his paintings, he prototypically represents the melancholy, which has been mentioned by his contemporaries and later biographers. Art scientists have also referred to his melancholy for the interpretation of his work. From a medical point of view, there are only two pathographies which remain inconclusive. Having applied diagnostic criteria for psychiatric disorders to his letters and publications, to statements of his contemporaries and to his art, we propose that he had suffered from a recurrent major depression which occurred in 1799 for the first time. At least three depressive episodes followed before he was struck by a stroke in 1835. There are epidemiological, psychodynamic and personality-typological reasons supporting our diagnostic assumption. The course of his depression corresponds to phases of reduced creativity, to the chosen techniques and motives. Finally we discuss the implications of our approach for the pathographical method in general.