A non-intrusive optical technique was employed to provide time-resolved images of the lower portion of the liquid film of horizontal annular flow of air and water, revealing the interfacial wave behavior. Time-resolved images of the pipe cross section revealed the dynamics of the complete liquid film around the pipe wall. The planar laser induced fluorescence technique (PLIF) was implemented to allow for the optical separation of the light emitted by the film from that (more intense) scattered by the air-water interface. The visualization test section was fabricated from a tube material which has nearly the same refractive index as water, what allowed for the visualization of the liquid film at regions very close to the pipe wall. Longitudinal images of the liquid film were captured using a high speed digital video camera synchronized with a high repetition rate laser. Data sets were collected with sampling camera frequencies ranging from 250 to 3000 Hz. A specially developed image processing algorithm was employed to automatically detect the position of the air-water interface in each image frame. The thickness of the liquid film was measured at two axial stations in each processed image frame, providing time history records of the film thickness at two different positions. Wave velocities were measured by cross-correlating the amplitude signals from the two axial positions. Wave frequency information was obtained by analyzing the time-dependent signals of film thickness recorded. The results obtained allowed for the verification of the variation of the liquid film characteristics with global flow parameters, such as the liquid and gas flow superficial velocities. For the film cross section observations, two high speed digital video cameras were used in a stereoscopic arrangement. The high repetition rate laser had its laser sheet mounted so as to illuminate a pipe cross section. Images from the left and right cameras were distorted by the use of a calibration target and an image correction algorithm. Distorted images from each camera were then joined to yield the complete instantaneous cross section image of the liquid film. Comparisons with results from different techniques available in literature indicate that the present technique presents equivalent accuracy in measuring the liquid film properties. The stereoscopic technique developed is an original contribution of the present work to the set of experimental techniques available for the study of two-phase flows. Time–resolved images of longitudinal and cross section views of the film were recorded and analyzed, what constitutes in valuable information for the understanding of the dynamics of the liquid film in horizontal annular flow.