In order to evaluate the possible impact of changes in Italian guidelines following the dissemination of the results of trials such as ACTG 5164, we analysed temporal changes of the time from a first diagnosis of ADE to the time of starting antiretroviral treatement in patients of the Icona Foundation Study cohort who were diagnosed with AIDS when ART-naive. In case of Afatinib multiple diagnoses, clinicians are asked to rank the illness in order of disease severity, and the most severe condition was used for classification in the analysis. ART was defined as a regimen of $1 drug belonging to one of the 3 major historical drug classes. Calendar periods of AIDS diagnosis were grouped as 1996– 2000, 2001–2008, and 2009+, the earliest period reflecting the years of old generation ART regimens typically with a heavy pill burden and lower tolerability, the latter period reflecting the years after the introduction of modern regimens and following the first presentation of the results of the ACTG 5164 trial at an International Conference. Standard survival analysis by Kaplan-Meier was used to estimate the cumulative percentage of people starting ART from the date of AIDS diagnosis. All KM plots have been truncated at 30 days. The threshold of 30 days were based on current treatment guidelines as well as assumptions. Thirty days is the maximum length of time whitin which is recommended to start ART after a diagnosis of all opportunistic conditions, except for tuberculosis and criptococcosis. Multivariable Cox regression model was used to investigate the association between calendar periods of diagnosis and type of ADE with time to ART initiation after controlling for age, gender, nation of birth, HIV transmission route, hepatitis co-infection status, reason for enrolment in the cohort, CD4 count at diagnosis and number of concomitant ADE. All demographics as well as laboratory markers that were associated in univariable analysis with a p-value = 0.15 were included in the multivariable model with the exception of CD8 and white blood cell counts which were collinear with CD4 counts. The results of our analysis show that in recent years Italian clinicians tend to initiate ART more promptly than in the past after a diagnosis of AIDS. Nevertheless, even in recent years the overall probability of starting ART seems to remain low with a median time to ART initiation of 21 days. Indeed, these estimates are considerably lower than what has been suggested as optimal time of starting ART on the basis of the results of the ACTG 5164 trial. Even in the subset of people who were diagnosed under prospective follow-up in the cohort, the estimate remains low. Of note, however, our estimates refer to any diagnosis of OI while in the trial 75% of patients had been diagnosed with Pcp and cases of TB were excluded.