Both antiretroviral treatment interruption (TI) and cessation have been strongly discouraged since 2006. We describe the incidence, duration, and risk factors for TI and loss-to-follow-up (LTFU) rates across 13 countries. All 4689 adults (76% men) in two large HIV cohorts in Australia and Asia commencing combination antiretroviral therapy (ART) to March 2010 were included. TI was defined by ART cessation >30 days, then recommencement, and loss to follow-up (LTFU) by no visit since 31 March 2009 and no record of death. Survival analysis and Poisson regression methods were used. With median follow-up of 4.4 years [interquartile range (IQR):2.1-6.5], TI incidence was 6.7 per 100 person years (PY) (95% CI:6.1-7.3) pre-2006, falling to 2.0 (95% CI:1.7-2.2) from 2006 (p<0.01). LTFU incidence was 3.5 per 100 PY (95% CI:3.1-3.9) pre-2006, and 4.1 (95% CI:3.5-4.9) from 2006 (p=0.22). TIs accounted for 6.4% of potential time on ART pre-2006 and 1.2% from 2006 (p<0.01), and LTFU 4.7% of potential time on ART pre-2006 and 6.6% from 2006 (p<0.01). Median TI duration was 163 (IQR: 75-391) days pre-2006 and 118 (IQR: 67-270) days from 2006 (p<0.01). Independent risk factors for the first TI were: Australia HIV Observational Database participation; ART initiation pre-2006; ART regimens including stavudine and didanosine; three nucleoside analogue reverse transcriptase inhibitors; ≥7 pills per day; and ART with food restrictions (fasting or with food). In conclusion, since 2006, 7.8% of patients had significant time off treatment, which has the potential to compromise any 'test and treat' policy as during the interruption viral load will rebound and increase the risk of transmission.