Autism Spectrum Disorder (ASD) was first described by Kanner in 1943, in which he emphasized the presence of a momentary displayof depression. ASD can affect as many as 1 in every 59 children. Most of the time, ASD is associated with comorbidities, such as Depressive Disorders (DD) that are one of the most common. Yet, there is no gold standard to assess DD among children or adolescents with ASD. Authors recommand the use of physiological or behavioral measures. In previous studies, sample sizes were small, girls or children and adolescents with an Intellectual Disability (ID) were rarely included. Authors stress the need to conduct studies to evaluate the fiability and validity of DD assessments. The aims of this study is to create and validate a screening scale of DD signs for children and adolescents with an ASD, identify associated factors and study common displays of depression among children and adolescents with an ASD. Four studies were completed. The first one aimed at creating and validating a screening scale of DD signs for children and adolescents with an ASD. It is divided into three parts : an assessment of pain and medication, a list of environmental changes, and an assessment of DD signs that is composed of two parts. The first part measures habitual behaviors and the second measures the extent of behavioral changes. The second study focused on validating this scale (N=153). Inter-judge reliability is excellent but must be tested on a bigger sample. Face, content and criterion validity is also satisfyng. Internal consistency is excellent. Exploratory Factor Analysis revealed two factors : the first one is composed of behavioral changes, and the second one of emotional and cognitive changes. The third study intended to identify associated factors to DD signs among youth with ASD (N=58). Children and adolescents with difficulties regarding social competence, emotional regulation, late diagnosis, hospitalizations and somatic diseases present more DD signs. Concerning family, parents with a history of mental illness, stress level and parental guidance needs, as well as school needs, such as teachers training on ASD, are associated with more DD signs. Finally, children and adolescents with an ASD that wish they had friends present more DD signs. The forth study aimed at describing DD features present in habitual behaviors of children and adolescents with an ASD (N=133). More than a third of the sample express sadness every day and more than a quarter never expresses happiness. Over half of the youth have anhedonia. One in five is self-agressive and 28% display hetero-agressive behaviors every day. Half of the sample experience sleep disorders and 58% have appetite troubles every day. Finaly, three quarters of the sample express feelings of guilt and worthlessness every day. DD features are linked to being open to experiences, hearing, social competence, emotional regulation, and family cohesion. To conclude, it is necessary to continue this study with a larger sample size and to identify associated factors of DD signs to ensure the psychometric qualities of the DD screening scale among children and adolescents with an ASD. All the results of this study make it possible to better identify depression and risk profiles among children and adolescents with ASD. Finally, from these findings, prevention and follow-up interventions may be proposed, based on factors associated with signs of depression.