7-Methylxanthine is a methyl derivative of xanthine, found occasionally in human urine. 7-Methylxanthine is one of the purine components in urinary calculi. Methylated purines originate from the metabolism of methylxanthines (caffeine, theophylline and theobromine). Caffeine is metabolized via successive pathways mainly catalyzed by CYP1A2, xanthine oxidase or N-acetyltransferase-2 to give 14 different metabolites, including 7-methylxanthine. CYP1A2 activity shows an inter-individual variability among the population. CYP1A2, an isoform of the CYP1A cytochrome P450 super-family, is involved in the metabolism of many drugs and plays a potentially important role in the induction of chemical carcinogenesis. Purine derivatives in urinary calculi could be considered markers of abnormal purine metabolism. The content of a purine derivative in stone depends on its average urinary excretion in the general population, similarity to the chemical structure of uric acid, and content of the latter in stone. This suggests that purines in stones represent a solid solution with uric acid as solvent. It is also plausible that methylxanthines, ubiquitous components of the diet and drugs, are involved in the pathogenesis of urolithiasis.