A positive Toxoplasma immunoglobulin M (IgM) result is often interpreted as a marker of an acute infection. However, IgM can persist for several years and Toxoplasma commercial IgM diagnostic test kits can yield a number of false positive results. For these reasons, a chronic Toxoplasma infection can be erroneously classified as an acute infection resulting in serious adverse consequences, especially in pregnant women, leading to emotional distress and unnecessary interventions including termination of pregnancy. Interpretation of Toxoplasma serology at a reference laboratory can help differentiate a recently acquired infection from a chronic infection. Serological test results in 451 patients with positive Toxoplasma IgM and IgG test results obtained at non-reference laboratories (NRLs) that were referred to Palo Alto Medical Foundation -Toxoplasma Serology Laboratory (PAMF-TSL) to determine whether patient was acutely or chronically infected were retrospectively reviewed. Of the 451 patients, PAMF-TSL results established that 335 (74%) had a chronic infection, 100 (22%) an acute infection, 7 (2%) were not infected and in 9 (2%) results were indeterminate. Positive Toxoplasma IgM and IgG test results performed at NRLs cannot accurately distinguish between acute and chronic infections. To do so, testing at reference laboratories is required as mandated in 1997 in a letter from the Food and Drug Administration (FDA) to clinicians and laboratories in the United States.