Recent advances in healthcare technologies along with improved medical care have led to a steady increase in life expectancy over the past few decades. As a result, the world population is aging rapidly. Various researches have been carried out to provide information and communication technologies based solutions that enhance the well-being of elderly people and provide them with a well margin of independency in their daily life. Ambient assisted living can be defined as the use of information and communication technologies in a person’s daily living and working environment to enable them to stay active longer, remain socially connected and live independently into old age. Since the information transmitted in ambient assisted living systems is very sensitive, the security and privacy of such data are becoming important issues that must be dealt with. In this paper, we propose a novel lightweight authentication protocol for the ambient assisted living systems. The proposed authentication protocol not only supports several important security requirements needed by the ambient assisted living systems, but can also withstand various types of attacks. In addition, the security analysis results show that the proposed authentication protocol is more efficient and secure than the existing authentication protocols.