A new evaluation method of unsteadiness of the spray generated by an effervescent atomizer is presented. The method is based on measurements of pressure fluctuations in the atomizer mixing chamber. Measurements, made under different atomizer operational conditions, show that the spray unsteadiness depends mainly on gas-to-liquid ratio (GLR). Decrease in GLR causes the spray to become more unsteady. The relation between atomizer internal two-phase flow pattern and the spray unsteadiness is elucidated by visualization of the internal two-phase flow using a digital camera and the use of published two-phase flow maps. Findings of the new method are complemented and confronted with the results obtained by the use of the spray unsteadiness evaluation method of Edwars and Marx.