Lupus nephritis (LN) is the most common cause of kidney injury in systemic lupus erythematosus and associated with higher morbidity and mortality. Low medication adherence correlates with adverse clinical outcomes. In a large, integrated health system at Kaiser Permanente East Bay Area, the authors identified mycophenolate mofetil (MMF) prescriptions for LN and collected patient demographics, medication adherence, and copay data. They interviewed patients with low medication adherence rates to understand contributing factors, such as side effects, cost, refill processes, and laboratory draws. Adherence was defined as a proportion of days covered at > 80%. The proportion of days covered is the number of days covered by a medication divided by the number of days in a defined period. Between November 30, 2021, and November 30, 2022, the authors identified 36 patients with LN on MMF. Almost a third (11/36) of these patients were nonadherent to medication. More than half (7/11) of these patients agreed to be interviewed. They identified the following causes of medication nonadherence: forgetfulness (57%, or 4/7), incomplete laboratory work (28%, or 2/7), medication cost (14%, or 1/7), and intentionally missed doses (14%, or 1/7). No patients identified medication side effects as a cause. The median 30-day copay for MMF was $4.55, and 28% (2/7) of patients paid $0 for their medications. In the authors' integrated health system, 69% of their patients with LN on MMF were adherent to their medication regimen. Forgetfulness was a challenge for the nonadherent patients. Kaiser Permanente East Bay Area provides convenient refills and laboratory draws; this likely facilitates medication adherence.