Functional analysis assessment procedures have proven to be highly useful in identifying variables maintaining aberrant behavior like self-injury. When successful, assessments can lead to more effective treatment than when behavioral function is unknown. Because of practical limitations, not all clinicians can conduct extensive and thorough analyses prior to treatment implementation. Although relatively brief assessments have proven successful in a number of published studies, it is unclear under what conditions those assessments would match the results of a more extended analysis. This study examined a method for assessing the behavioral function of severe self-injury in four adult participants. For each participant, the initial assessment involved analyzing within-session trends and fluctuations in rates of self-injury by plotting the frequency within each minute of a session. The results of these analyses were then compared to a set of more traditional, longer-term functional analyses conducted with each participant. Results suggested that within-session analyses are viable procedures for the assessment of self-injury. Potential benefits of within-session analyses over other brief assessments and longer-term analyses are discussed.