Variants at the gene encoding for the 5-hydrosytryptamine (serotonin) receptor 2A (HTR2A) have been associated with many psychiatric disorders such as schizophrenia, mood disorders, attention deficit hyperactivity disorder, suicide, anxiety disorders, obsessive-compulsive disorder, eating disorders, and Alzheimers disease. The studied SNPs differ across studies, in the present review we focused on available evidence with the aim of identifying the overall phenotypic profile of HTR2A variant carriers. We then extensively analyzed all SNPs of the HTR2A gene with criteria of frequency, haplotype blocks, previous evidence, functionality in order to obtain a list of suitable SNPs for future studies that properly cover all possible genetic control of the HTR2A gene. Genetic association studies report conflicting and generally negative results. Most replicated data suggest C allele of the 102 T/C and Tyr452 variants as risk factor for psychosis and antipsychotic response, but the number of not replicating studies does not allow to draw any definite conclusion. Moreover their impact as risk factors is very small. In the other investigated psychiatric fields, evidence shows no involvement or at least a small and not replicated role for HTR2A gene variants. Conflicting and negative results could be due to a real marginal role of this receptor gene variants, or it could be caused by a lack of gene coverage of investigated SNPs. We suggest a wider investigation of the HTR2A gene to better understand its role in psychiatric disorders, preferably complemented with the use of proteomic or metabolomic approaches.