The paper presents an overview of an ethological approach to the study of abnormal human behavior and a review of research using ethological approaches (with an emphasis on autism research). Ethology is defined as the study of behavior as it occurs in its natural habitat. The four types of questions ethologists ask about behavior, such as what is the immediate causation of a behavior pattern, are discussed. Seven research methodologies, including ad libitum sampling and sequence sampling, are defined. Areas of interest to ethologists and representative studies in the areas are examined. Ethological approaches to psychopathology are reviewed, and the distinction between comparative psychology and ethological studies is made. The ethological view of autism, which emphasizes nonverbal aspects such as gaze aversion and stereotypic behavior, is explored. (PHR)