Papillon-Lefèvre syndrome (PLS; OMIM: 245000) is a rare disease characterized by severe periodontitis and palmoplantar keratoderma. It is caused by mutations in both alleles of the cathepsin C (CatC) gene CTSC which completely abrogate the proteolytic activity of this cysteine proteinase. A genetic analysis most often is unaffordable or unavailable to establish an early rapid diagnosis of PLS. In this study, we tested the hypothesis that active CatC is constitutively excreted and can be easily traced in the urine of normal subjects. If true, its absence in the urine of patients would be an early, simple, reliable, low cost and easy diagnostic technique. All 75 urine samples from healthy control subjects (aged 3 months to 80 years) contained proteolytically active CatC and its proform as revealed by kinetic analysis and immunochemical detection. From the urine samples of 31 patients with a PLS phenotype, 29 contained neither proteolytically active CatC nor the CatC antigen so that the PLS diagnosis was confirmed. CatC was detected in the urine of the other two patients and genetic analysis revealed no loss-of-function mutation in CTSC indicating that they suffer from a PLS-like condition but not from PLS. Screening the absence of urinary CatC activity soon after birth and early treatment before the onset of PLS manifestations will help to prevent aggressive periodontitis and loss of many teeth and should considerably improve the quality of life of PLS patients.