This study examined the association of appointment nonadherence to markers of disease severity using one year of demographic and health information on 995 individuals with HIV in primary care at an urban community health centre. At the latest visit, 106 of 946 valid cases (11.2%) had a CD4 less than or equal to 200, and 454 of 936 valid cases (48.5%) had detectable plasma HIV RNA (greater than 50 copies/ml). Using logistic regression, appointment nonadherence (number of missed appointments) was a significant predictor (p<.03) of having an AIDS-defining CD4 count over and above the effects of number of kept appointments (p<.0001), and whether or not the patient was taking HAART (p<.002). Appointment nonadherence was also a significant predictor (p<.05) of having a detectable viral load over and above the effects of number of kept appointments (p<.003), HAART (p<.0001) and age (p<.004). Looking only at individuals with a detectable viral load at the earliest visit, the only significant unique predictor of improvement to an undetectable viral load at the latest visit was being on HAART (p<.05). Looking at those only with an undetectable viral load at the earliest visit, the only predictor of declining to a detectable viral load was number of kept appointments (p < 003), and being on HAART (p<.05).