Sexual orgasm is achieved without pain or humiliation. Class III: Masochists with minimal to no sadistic tendencies. Preference for pain or humiliation (which facilitates orgasm), but not necessary to orgasm. Capable of romantic attachment. Class IV: Exclusive masochists (i.e. cannot form typical romantic relationships, cannot achieve orgasm without pain or humiliation).Sexual sadists:

Class I: Bothered by sexual fantasies but do not act on them. Class II: Act on sadistic urges with consenting sexual partners (masochists or otherwise). Categorization as leptosadism is outdated. Class III: Act on sadistic urges with non-consenting victims, but do not seriously injure or kill. May coincide with sadistic rapists. Class IV: Only act with non-consenting victims and will seriously injure or kill them.The difference between I–II and III–IV is consent. BDSM
The term BDSM is commonly used to describe consensual activities that contain sadistic and masochistic elements. Masochists tend to be very specific about the types of pain they enjoy, preferring some and disliking others. Many behaviors such as spanking, tickling, and love-bites contain elements of sadomasochism. Even if both parties legally consent to such acts this may not be accepted as a defense against criminal charges. Very few jurisdictions will permit consent as a legitimate defense if serious bodily injuries are caused. It has been argued that in many countries, the law disregards the sexual nature of sadomasochism - or the fact that participants enter these relationships voluntarily because they enjoy the experience. Instead, the criminal justice system focuses on what it views as dangerous or violent behavior.
"Based on advances in research and clinical practice, and major shifts in social attitudes and in relevant policies, laws, and human rights standards", the World Health Organization (18 June 2018) removed Fetishism, Transvestic Fetishism and Sadomasochism as psychiatric diagnoses.The ICD-11 classification consider Sadomasochism as a variant in sexual arousal and private behavior without appreciable public health impact and for which treatment is neither indicated nor sought. "Further the ICD-11 guidelines "respect the rights of individuals whose atypical sexual behavior is consensual and not harmful. "WHOs ICD-11 Working Group admits that psychiatric diagnoses have been used to harass, silence, or imprison sadomasochists. Labeling them as such may create harm, convey social judgment, and exacerbate existing stigma and violence to individuals so labeled.According to ICD-11, psychiatric diagnoses can no longer be used to discriminate against BDSM people and fetishists.Recent surveys on the spread of BDSM fantasies and practices show strong variations in the range of their results. Nonetheless, researchers assume that 5 to 25 percent of the population practices sexual behavior related to pain or dominance and submission. The population with related fantasies is believed to be even larger. Forensic classification
According to Anil Aggrawal, in forensic science, levels of sexual sadism and masochism are classified as follows:
Sexual masochists:

Class I: Bothered by, but not seeking out, fantasies. May be preponderantly sadists with minimal masochistic tendencies or non-sadomasochistic with minimal masochistic tendencies
Class II: Equal mix of sadistic and masochistic tendencies. Like to receive pain but also like to be dominant partner (in this case, sadists).