Many classification systems have been developed for lymphomas, and experts disagree on exactly how they should be organized. The most recent classification system was developed by the World Health Organization (WHO). Whereas previous classification systems mainly relied on the appearance of the lymphoma cells, the WHO system relies on the genetic and chemical characteristics of the cells as well.

Types of non-Hodgkin’s lymphoma are first divided by cell type into B-cell or T-cell groups. They are then further classified by whether the tumors were derived from precursor (immature) or peripheral (mature) cells.

Non-Hodgkin's lymphoma is generally classified as:

• B-cell neoplasms
  
  
• Precursor B-cell neoplasm
  
  
• Peripheral B-cell neoplasms
  
  
• Includes B-cell chronic lymphocytic leukemia/small lymphocytic leukemia, mantle cell lymphoma, hairy cell leukemia and Burkitt's lymphoma
  
  
• T-cell and putative natural killer cell (NK-cell) neoplasms
  
  
• Precursor T-cell neoplasm
  
  
• Peripheral T-cell and NK-cell neoplasms
  
  
• Includes T-cell chronic lympocytic leukemia/prolymphoctic leukemia, T-cell granular lympocytic leukemia and peripheral T-cell lymphoma

Though there are many types of NHL, two forms are the most common. These include:

• Diffuse large cell B-cell lymphoma (DLBCL). DLBCL accounts for approximately three out of 10 cases of lymphoma. Occurring mostly in older people, this cancer often grows rapidly.
  
  
• Follicular lymphoma. Occurring mostly in adults, this form accounts for approximately two out of 10 cases of lymphoma. It is a slow-growing cancer in which the cells usually grow in a circular pattern in the lymph nodes.

According to the American Cancer Society (ACS), DLBCL and follicular lymphoma account for more than half of all cases of lymphoma.

Non-Hodgkin’s lymphomas can also be described in terms of how aggressive they are and the location of affected lymph nodes. NHL may be described as:

• Indolent or aggressive
  
  
• Indolent lymphomas, also known as low-grade lymphomas,  usually have few symptoms and grow and spread slowly.
  
  
• Aggressive lymphomas, also known as intermediate-grade and high-grade lymphoma, usually have severe symptoms and grow and spread rapidly.
  
  
• Contiguous or noncontiguous
  
  
• Contiguous lymphomas are lymphomas in which the cancer containing lymph nodes are located next to each other.
  
  
• Noncontiguous lymphomas are lymphomas in which the cancer containing lymph nodes are not next to each other, but are on the same side of the diaphragm (a muscle that separates the chest and abdominal cavities). For example, lymphomas in lymph nodes under the right arm and in the right groin area are noncontiguous.