A Ph. Eur. herbal drug monograph requires for identification testing besides macroscopic (A) and microscopic (B) evaluation a thin-layer chromatography (TLC) fingerprint, prescribed as identification testing in subsection C. The main active constituents of Cassia senna L. and Cassia angustifolia Vahl are the dianthrone glucosides (mainly sennoside A and B). Therefore, this study presents a high-performance thin-layer chromatography (HPTLC) method which uses the sennosides as characteristic constituents. The presented method results in a fast and simple fingerprint with characteristic yellow fluorescence for the sennosides due to derivatization with a potassium hydroxide solution. The use of a senna herbal drug dry extract as system suitability test (SST) allows for a cost-effective test control. The resolution of the sennosides zones is dependent on the extractives concentration. An overload of the analytes leads to tailing (u-shaped form) and broadening as well as change in the retardation factor (RF). The presented method is a suitable fingerprint method for Ph. Eur. conform identification C.