Autism spectrum disorders (ASDs) are a group of neurodevelopmental disorders including autistic disorder, Asperger syndrome, and pervasive developmental disorder not otherwise specified as to Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition. All these categories are grouped together in Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, classification under the category of Autism Spectrum Disorders.Behavioral disorders including irritability, attention-deficit/hyperactivity disorder (ADHD) symptoms, and aggression are additional symptoms found in up to 20% of children and adolescents with ASD and require careful evaluation for appropriate treatment. Attention-deficit/hyperactivity disorder is defined by impaired attention, hyperactivity, and impulsivity, whereas ASD is defined by social dysfunction, communicative impairment, and restricted/repetitive behaviors. They should be distinctly evaluated in children and adolescents with ASD and intellectual disability in contrast to individuals without intellectual disability, because significant differences between these conditions exist. Mood disorders are also common in ASD and should be systematically investigated in this population of children and adolescents. Approximately 50% of children and adolescents with ASD receive medication for comorbid behavioral/ADHD and mood symptoms, mostly stimulants, antiepileptics and antipsychotics. Guidelines for the evaluation and treatment including medications for ADHD-like symptoms have recently been provided and should be carefully considered. Antiepileptic drugs are commonly used in ASDs with epilepsy, because seizures are associated with ASD in 10% to 30% of young patients, and as mood stabilizers. Lithium is another option for children and adolescents with ASD who present with symptoms of a mood disorder, such as elevated moods/euphoria, mania, and paranoia, whether accompanied or not by irritability. Experimental treatments are under investigation and currently include arbaclofen, a γ-aminobutyric acid agent, and N-acetylcisteine, a glutamate agent.