Within the major therapeutic paradigms, observational instruments have been developed to assess orientation-specific interventions or processes. However, to date, no such instrument exists to assess existential practices. Recent research indicates the key practices of existential therapists, and forms an empirical basis on which to develop an observatory grid. This paper describes the development of such a grid, and its exploratory testing with eight clients of four Portuguese existential psychotherapists. A total of 32 sessions were observed and both speaking turn and whole session analysis showed that it was feasible to assess existential therapy using the instrument, although psychometric findings recommend further refinement of the tool. Session rating data suggests that the chief practices applied by existential therapists were relational, followed by the use of hermeneutic interventions and reformulations. Interventions based on phenomenological and existential assumptions were observable in practice but limited in frequency. Further refinements and developments of the observational grid, together with additional research – using a range of therapists from different schools of existential therapy – are recommended. © 2016. This is an author produced version of a paper published in the British Journal of Guidance and Counselling uploaded in accordance with the publisher’s self- archiving policy (embargoed until 04/11/2017). The final published version (version of record) is available online via Taylor & Francis athttp://www.tandfonline.com/doi/full/10.1080/03069885.2016.1254723. Some minor differences between this version and the final published version may remain. We suggest you refer to the final published version should you wish to cite from it.