We present 11 maps of BL Lacertae object 1803+784 derived from geodetic VLBI observations archived at the Washington Correlator. The observations were obtained during the years 1988-1999. In this period three superluminal components with an expansion rate of 0.084 mas yr-1 were identified. A remarkable feature of the VLBI images is that the superluminal components only become visible on the jet at a radius of 1 mas from the core, which was interpreted as a result of a helically curved jet. This feature and further evidence of helical patterns found in published high dynamic range VLBI maps at parsec scale and kiloparsec scale enabled us to obtain a well-constrained helical jet. The overall radio morphology of 1803+784 could be described by two dominant components given by a narrow helical jet extending east-west about 6 kpc from the core (deprojected size of 30 kpc) and a much larger north-south component perpendicular to the helical jet (cone axis) with a linear size of about 270 kpc.5732 I496504Antonucci, R.R.J., Hickson, P., Olsezewski, E.W., Miller, J.S., (1986) AJ, 92, p. 1Biermann, P., (1981) ApJ, 247, pp. L53Britzen, S., Krichbaum, T.P., (1995) Proc. 10th Working Meeting on European VLBI for Geodesy and Astrometry, p. 172. , ed. R. Lanotte & G. Bianco (Matera: ASI)Britzen, S., Witzel, A., Krichbaum, T.P., Muxlow, T.W.B., (1999) NewA Rev., 43, p. 751Carter, W.E., Robertson, D.S., MacKay, J.R., (1985) J. Geophys. Res., 90, p. 4577Charlot, P., (1990) A&A, 229, p. 51Coates, R.J., Frey, H., Mead, G.D., Bosworth, J.M., (1985) IEEE Trans. Geosci. & Remote Sensing, GE-23, p. 360Conway, J.E., Murphy, D.W., (1993) ApJ, 411, p. 89Eubanks, T.M., (1991) Earth Orientation...Program, p. 73. , IERS Tech. Note 8Paris: IERSFey, A.F., Clegg, A.W., Fomalont, E.B., (1996) ApJS, 105, p. 299Gabuzda, D.C., (2000) Astrophysical Phenomena Revealed by Space VLBI, p. 121. , ed. H. Hirabayashi, P. G. Edwards, & D. W. Murphy (Sagamihara: Inst. Space & Astronautical Sci.)Gabuzda, D.C., Cawthorne, T.V., (1996) MNRAS, 283, p. 759Gabuzda, D.C., Cawthorne, T.V., Roberts, D.H., Wardle, J.F.C., (1992) ApJ, 388, p. 40Gabuzda, D.C., Mullan, C.M., Cawthorne, T.V., Wardle, J.F.C., Roberts, D.H., (1994) ApJ, 435, p. 140Ghisellini, G., Padovani, P., Celotti, A., Maraschi, L., (1993) ApJ, 407, p. 65Hardee, P.E., (1987) ApJ, 318, p. 78Higgins, S.W., O'Brien, T.J., Dunlop, J.S., (1999) MNRAS, 309, p. 273Kellermann, K.I., Vermeulen, R.C., Zensus, J.A., Cohen, M.H., (1998) AJ, 115, p. 1295Kollgaard, R.I., Wardle, J.F.C., Roberts, D.H., Gabuzda, D.C., (1992) AJ, 104, p. 1687Krichbaum, T.P., Witzel, A., Graham, D.A., Schalinski, C.J., Zensus, J.A., (1993) Subarcsecond Radio Astronomy, p. 260. , ed. R. J. Davies & R. S. Booth (Cambridge: Cambridge Univ. Press)Lähteenmäki, A., Valtaoja, E., (1999) ApJ, 521, p. 493Lawrence, C.R., Zucker, J.R., Readhead, A.C.S., Unwin, S.C., Pearson, T.J., Xu, W., (1996) ApJS, 107, p. 541Pearson, T.J., Readhead, A.C.S., (1984) ARA&A, 22, p. 97(1988) ApJ, 328, p. 114Qian, S.J., Krichbaum, T.P., Zensus, J.A., Steffen, W., Witzel, A., (1996) A&A, 308, p. 395Rogers, A.E.E., (1983) Science, 219, p. 51Ros, E., Marcaide, J.M., Guirado, J.C., Ratner, M.I., Shapiro, I.I., Krichbaum, T.P., Witzel, A., Preston, R.A., (1999) A&A, 348, p. 381Smith, D.E., Turcotte, D.L., (1993) Geodynamics Ser., 23. , Contributions of Space Geodesy to Geodynamics: Crustal Dynamics (Washington: AGU)Stocke, J.T., Burns, J.O., Christiansen, W.A., (1985) ApJ, 299, p. 799Strom, R.G., Biermann, P.L., (1991) A&A, 242, p. 313Tateyama, C.E., Kingham, K.A., Kaufmann, P., Piner, B.G., Botti, L.C.L., De Lucena, A.M.P., (1999) ApJ, 520, p. 627Tateyama, C.E., Kingham, K.A., Kaufmann, P., Piner, B.G., De Lucena, A.M.P., Botti, L.C.L., (1998) ApJ, 500, p. 810Valtaoja, E., Lähteenmäki, A., Teräsranta, H., Lainela, M., (1999) ApJS, 120, p. 95Vicente, L., Charlot, P., Sol, H., (1996) A&A, 312, p. 727Wagner, S.J., Witzel, A., (1995) ARA&A, 33, p. 163Wehrle, A.E., Piner, B.G., Unwin, S.C., Zook, A.C., Xu, W., Marscher, A.P., Teräsranta, Valtaoja, E., (2001) ApJS, 133, p. 297Witzel, A., Schalinski, C.J., Johnston, K.J., Biermann, P.L., Krichbaum, T.P., Hummel, C.A., Eckart, A., (1988) A&A, 206, p. 245