Pain is an accompanied problem for many pathologic conditions and diseases. Such sensations disappear gradually when related to acute pathology or trauma. However, pain can became chronic and acquire traits of self-sustained disease. In practice, many characteristics can be useful for estimation of pain sensation, and the goal of this paper is to analyze of modern methods for intensity pain assessment in adults and children, of interpretation of pain estimation, and of possible algorithm for next steps. In majority cases, pain intensity is changing parameter. Therefore, pain assessment is performed in some standard points of time. For a quantitative assessment of pain, a scale is proposed to help the patient, relative to the extreme points of which a pointer can be placed indicating the relative severity of his sensations. For such purpose visual analog scale, numeric rating scale, and verbal numeric scale can be used. The Wong-Baker Faces Pain Rating Scale, the FLACC scale, the CRIES pain scale can be exploited in small children. In this population the CHEOPS scale, the OPS scale, and the COMFORT scale were recommended to apply after surgery. The final step of interpretation implies that quantitative data converts to ratings. The last ones form to basis of WHO analgesic ladder that is exploited for drugs selection to treat pain, in particular in patients with cancer pain or postoperative pain. From this approach, moderate and severe pain recommends to administer full opioid agonists. However, today there is a good alternative in the form of selective mu1-receptots agonist, which has lower risk of side opioid effects. Thus, in this time, there is some progress in pain management. This progress, in our opinion, is due to improved analysis of the condition of patients suffering from moderate and severe pain, and the emergence of new opioid agonists with high selectivity for the mu1 subclass of opioid receptors.