Publications from the 1990s reported high variability in the particle size and respirable fraction of aerosol from nebulizers. In recent years, many innovations in nebulizer design have occurred, intended to reduce treatment times, improve respirable doses, and reduce variability. In this study, a range of nebulizers with different designs were characterized in terms of mass median diameter (MMD) and fine particle fraction (FPF; % of particles <5 μm) using laser diffraction. Nine nebulizers were selected for testing: conventional jet nebulizers (Salter 8900 Series, Salter Labs, Arvin, CA, USA; SideStream, Respironics Respiratory Drug Delivery (UK) Ltd, Chichester, UK); breath-enhanced jet nebulizers (LC Plus, PARI GmbH, Starnberg, Germany; LC Sprint, PARI GmbH; SideStream Plus, Respironics Respiratory Drug Delivery (UK) Ltd); a breath-activated jet nebulizer (AeroEclipse II, Monaghan Medical Corp., Plattsburgh, NY, USA); non-breath-enhanced vibrating mesh devices (eFlow rapid, PARI GmbH; MicroAir U22, OMRON Healthcare, Kyoto, Japan); and a breath-activated and monitoring mesh nebulizer (I-neb Adaptive Aerosol Delivery System, Respironics Respiratory Drug Delivery (UK) Ltd, Chichester, UK). It was concluded that there remains a high variability in the MMD and FPF of aerosols produced from nebulizers, which has not changed significantly since the 1990s, despite new developments. Selection of a nebulizer by its performance characteristics, including MMD and FPF, is as important now as in the past. Variability in nebulizer performance, in terms of particle size, may have clinical implications.