High-speed microwave chemistry has attracted considerable attention in the past two decades with new and innovative applications in organic and peptide synthesis, polymer chemistry, material sciences, nanotechnology and biochemical processes continuously being reported in the literature. In particular the introduction of benchtop single-mode microwave reactors just over ten years ago has revolutionized the way many scientists today perform reactions in the laboratory. Unfortunately, the accurate measurement of reaction temperature in these devices is far from being trivial and requires both a basic understanding of microwave dielectric heating effects and use of appropriate temperature monitoring devices. In this tutorial review frequently occurring problems in the determination of accurate reaction temperatures in single-mode microwave reactors are discussed.