Measurement of liquid droplet size distributions has many industrial applications, including sprays, wind tunnels, and demisters. Laser diffraction is one of the few available techniques that is widely used for the measurement of droplet size distributions. Although the technique is simple to use, it is not free from problems. This article describes the practical problems encountered when the technique was used to measure the drop sizes in three different experimental setups. Residual drop sizes due to the aerodynamic breakup of drops in a wind tunnel were measured. The objective of the experiment was to enhance our understanding of the breakup mechanism. In the second experiment, liquid drop size distributions in an inclinable two-phase flow were measured. The main interest was to investigate the impact of inclination on the drop size distributions for various flow conditions. In the third experiment, measurements were made in a narrow channel of a zigzag passage most often used in demisters. Because of the small size of the passage, liquid drops appeared almost instantly on the optical windows, prohibiting any laser measurements. Other problems include glass reflections and vibration as the laser system was mounted on different rigs. In this article some practical suggestions are made to overcome these problems, and some useful results are included.