Primary Objective: The relationship between prior mild traumatic brain injury/injuries (MTBI) and recovery from a subsequent MTBI may be complex. The present study investigated three factors hypothesized to influence this relation: (i) the number of prior MTBIs, (ii) the interval between MTBIs, and (iii) the certainty level of prior MTBIs. Research Design: Retrospective cross-sectional. Methods and Procedure: Participants (N=105) were evaluated at a concussion clinic on average one month after sustaining an MTBI, defined by World Health Organization diagnostic criteria. Main Outcomes and Results: Approximately half the sample had at least one prior MTBI. Subgroups with 0, 1, or 2+ prior MTBIs did not differ in levels of current postconcussion symptom reporting on the British Columbia Postconcussion Symptom Inventory. Time since the most recent prior MTBI was significantly associated with current postconcussion symptom reporting. This relation was best characterized as logarithmic, i.e., the impact of prior MTBI(s) lessens exponentially as time elapses to a subsequent MTBI. Defining prior MTBIs with a higher certainty level (i.e., probable versus possible) was not consistently associated with greater postconcussion symptom reporting. Conclusions: Participants with prior MTBIs did not report more postconcussion symptoms than those with no history of prior MTBI. However, prior MTBI(s) were associated with increased symptom reporting from a subsequent MTBI to the extent they occurred closer in time. Having one or two prior remote MTBIs was not associated with worse outcome from subsequent MTBI in this sample.