Executive summary Background: Injecting drug use is associated with high risk of tuberculosis (TB) and reduced retention in treatment. Provision of opioid substitution therapy (OST) improves HIV and TB treatment outcomes among people who inject drugs (PWID) but there is a lack of documented strategies for the effective delivery of integrated HIV, TB and drug dependency treatment. Within a harm reduction framework, Portugal has made concerted efforts to move towards integrated service delivery. We aimed to document existing models of integrated TB and HIV care for PWID in Porto, Portugal. Methods: We undertook a rapid assessment combining the following methods and data sources: a mapping of existing HIV, TB, hepatitis C virus (HCV) and drug dependency treatment services in Porto; a review of existing data on HIV, TB and drug treatment service use and integration; semi-structured interviews with 30 PWID with experience of HIV and/or TB, and with seven providers representing HIV, TB, drug treatment, outreach and prison health services. We analysed quantitative data descriptively and qualitative data thematically, triangulating findings throughout data collection and analysis. Findings: The assessment documented two models of integrated HIV, TB and drug dependency care for PWID. The first ‘combined’ model provides all services within a designated centre staffed by a co-located team of specialists with shared case management protocols. This approach facilitates multidisciplinary care but is resource-intensive, limited to a specific location and offers reduced scope for community/home-based care. The second ‘collaborative’ model is a less formalised, client-centred approach in which multiple and existing health programmes work together to achieve co-located treatment delivery in a location convenient to the patient, with outreach teams often acting as mediators between services. This model allows prompt access and adaptability to clients’ circumstances but is highly dependent on the participation of multiple services. The relative success of integration was shaped by four key factors: the extent of collaborative networks and shared protocols; the central involvement of outreach teams; provision of uninterrupted OST; and flexibility over treatment location. Engagement in services more broadly was shaped by social network and outreach support; recognition of patient autonomy; patient-provider relationships; timing of testing and treatment provision; treatment literacy; and the availability of social care. Few quantitative data were available to assess service integration. Targeted rapid HIV testing in drug treatment centres has achieved high coverage among PWID but rates of TB and HCV screening were low and incompletely reported. Most TB patients knew their HIV status but no equivalent data were available on TB among patients receiving HIV care. Recommendations: Guidelines on integration of HIV, TB and drug dependency care should reflect the importance of: multi-agency collaboration, use of existing professional networks to develop mechanisms for expedited access to integrated care; uninterrupted provision of drug dependency treatment accounting for interactions with anti-TB and anti-retroviral therapy; a client-centred approach recognising service users’ autonomy; and the key role outreach programmes can play in facilitating access. Recommendations specific to Porto include expansion of TB and HCV screening among PWID; improved health information systems; streamlined referral mechanisms; increased user involvement; renewed focus on HCV; tackling stigma in primary care; and addressing PWIDs’ broader social care needs.