The technique of reversible data hiding recovers the original image from a stego-image without distortion after the hidden data are extracted. A natural image usually contains several smooth areas. The difference between two adjacent pixels has a high probability of being a small value. Therefore, this study proposed a novel reversible data hiding method, Adjacent Pixel Difference (APD), which employs the histogram of the pixel difference sequence to increase the embedding capacity. Experimental results reveal that APD achieves a high embedded capacity and still maintains a high stego-image quality. Furthermore, the stego-image quality and embedded capacity of the APD method outperform those of NSAS, F&S and T&H.