Treatment abandonment, the failure to complete therapy that is required for definitive disease control, frequently causes treatment failure for pediatric patients in low- and middle-income countries with chronic conditions, particularly cancer. Other forms of incomplete treatment affecting children in all settings, such as nonadherence and loss to follow-up, are often confused with treatment abandonment. Unclear definitions of incomplete treatment dramatically affect reported outcomes. To facilitate disease-specific and cross-sector analyses, we outline a practical approach to categorize forms of incomplete treatment, present distinct semantic categories with case examples and provide an algorithm that could be tailored to disease- and context-specific needs. Pediatr Blood Cancer 2015;62:565–570. © 2015 Wiley Periodicals, Inc.