A study of the interaction of Lamb waves with a circular defect is presented. The Lamb wave mode chosen was the S0mode in the low frequency‐thickness regime excited by a circular source. A three dimensional Finite Element model was used to simulate the reflection behaviour. Experimental results were also obtained using an array transducer. Circular holes of 50&percent; depth and various diameters were studied. The specular reflection of an incident S0wave was predicted and compared with the experiments. The significance of the path lengths, wavelengths and defect sizes on the reflection characteristics were assessed. © 2003 American Institute of Physics