Measurement and control of the On-line diameter of filter rods and cigarettes has always been a major concern to the tobacco industry. Current methods using air gauges are limited in their response, scope and accuracy due to the inherent characteristics of the product and the method of measurement itself. All of the aforementioned problems have been overcome with off-line devices such as the Tape Gauge an LaserMike which provide laboratory accuracy and precision on the factory floor. The on-line version of the LaserMike, the System 5000 is a result of many years experience and knowledge in applying on-line measurement and statistical process control (SPC) in the continuous process industries such as fibre optic, medical tubing and wire and cable. The System 5000 has been designed as a retrofit item to replace existing air gauge units. The System 5000 has undergone an extensive period of development prior to its release in the Tobacco Industry. Extensive trials have been carried out at several sites and data is presented to show significant reduction in long term diameter variability. Work is in hand to evaluate the system further which should lead to improvement in the control of other physical properties. Following the success of this project it is expected to extend this work to the measurement and control of cigarette rod diameter.