This project determined the stable isotopic compositions (δ2H/δ13C/δ15N) of 181 samples of high purity illicit methylamphetamine seized in Queensland between July 2015 and February 2017. The project was undertaken to augment existing stable isotopic composition data for methylamphetamine samples seized at Australian borders. Based on a rule-of-thumb developed by the National Measurements Institute of Australia a majority of Queensland samples (~88%) were classified as being manufactured from synthetic ephedrine/pseudo-ephedrine (e.g. from 1-phenyl-1-propanone). A much smaller number of samples (~12%) were initially classified as being manufactured from natural ephedrine/pseudo-ephedrine (from Ephedra sinica). Subsequent analysis of samples classified as having a natural precursor found them to be enantiomerically pure l-methylamphetamine and, therefore, most likely manufactured from phenylpropan-2-one. In contrast to border seizures, no methylamphetamine seizures from Queensland had isotopic compositions consistent with being manufactured from semi-synthetic ephedrine/pseudo-ephedrine (fermentation of benzaldehyde and pyruvic acid). A small number of enantiomerically pure d-methylamphetamine samples with δ15N values intermediate between natural and synthetic classification were also assumed to be derived from phenylpropan-2-one. These samples were isotopically similar to seizures reported in Japan that had been imported from Eurasia. The combination of δ2H, δ13C and δ15N measurements was used to create a searchable database that identified a number of isotopically similar samples of methylamphetamine seized at different locations and different times. A kernel density estimate model was used to assign “moderately-strong” to “strong” support that these samples came from the same synthetic batch.