The availability of a large, well-characterized population enabled us to examine the relationship between environmental exposures before illness onset and phenotypes in JIIM. We confirmed a number of exposures that had also been seen in prior studies of JDM, particularly the temporal association of respiratory infections preceding illness onset [16, 17] . We identified for the first time that a number of other non-infectious exposures occurred within 6 months of the first signs of illness, including medications, many of which are potentially myopathic or photosensitizing, immunizations, stressful life events and sun exposure. The main novel findings of this study were differences in some exposures by age at diagnosis, delay to diagnosis, race, disease course and autoantibody phenotypes. For example, children younger than the median age at the time of diagnosis had a higher frequency of documented infections, whereas older children had a higher frequency of stressful life events in the months before illness onset. Patients without a myositis autoantibody had a higher frequency of infections in the 6 months before illness onset than was seen in patients with anti-p155 or anti-SRP autoantibodies, whereas patients with anti-SRP autoantibodies had a greater number of documented exposures than patients without a myositis autoantibody. These findings suggest that environmental exposures may differ by phenotype, and that they could be useful in understanding pathogeneses [1] . We found that an infectious illness, particularly a respiratory infection, frequently occurs within several months before juvenile myositis onset, supporting the findings of other studies of exposures temporally associated with the onset of JDM. In one study, a prospective registry of patients within 6 months of illness onset in which data were based on a parent environmental interview and medical record review, respiratory infections were identified within 3 months of illness onset in 57% of patients [16] . The other, a retrospective cohort with review of medical records by infectious disease specialists, identified infections within 3 months before Conventions as per Table 2 . Bold values represent P 4 0.05 after Holm's adjustment for multiple comparisons (using family-wise error rates of 5%). a Based on total number of drug exposures, because some patients had >1 documented drug exposure. Potentially myopathic drugs included penicillin (n = 2) and ranitidine (n = 1) [28] [29] [30] [31] . Potentially photosensitizing drugs included loratadine (n = 1), diphenhydramine (n = 1) and sertaline (n = 1) [26, 27] . Drugs classified as potentially both myopathic and photosensitizing included ibuprofen (n = 5), trimethroprim/sulphamethoxazole (n = 3), isoniazid (n = 2) and erythromycin-sulfisoxazole (n = 1). Drugs not known to be either myopathic or photosensitizing included amoxicillin (n = 4), cefaclor (n = 3), pseudoephedrine (n = 2), cetirizine (n = 1), albuterol inhaler (n = 1), flecainide (n = 1), bromopheniramine maleate (n = 1), nedocromil (n = 1), oxybutynin (n = 1), permethrin (n = 1), pyrethrine (n = 1), cantharidine (n = 1), cefadroxil (n = 1), acetaminophen (n = 1), streptomycin (n = 1), erythromycin (n = 1) and nystatin (n = 1). Drugs whose classification is unknown included unknown antibiotic (n = 10), birth control (n = 3) and anaesthetic (n = 1). *P = 0.004; OR 15.4; 95% CI 1.8, 135. y P = 0.008 ; OR 18.9; 95% CI 1.0, 358.